diff --git a/tests/baselines/reference/mappedTypesArraysTuples.js b/tests/baselines/reference/mappedTypesArraysTuples.js
index 5546f5201df..7bd4b03a6e5 100644
--- a/tests/baselines/reference/mappedTypesArraysTuples.js
+++ b/tests/baselines/reference/mappedTypesArraysTuples.js
@@ -28,6 +28,14 @@ type B = { b: string };
 
 type T40 = Boxified<A | A[] | ReadonlyArray<A> | [A, B] | string | string[]>;
 
+type ReadWrite<T> = { -readonly [P in keyof T] : T[P] };
+
+type T50 = Readonly<string[]>;
+type T51 = Readonly<[number, number]>;
+type T52 = Partial<Readonly<string[]>>;
+type T53 = Readonly<Partial<string[]>>;
+type T54 = ReadWrite<Required<T53>>;
+
 declare function unboxify<T>(x: Boxified<T>): T;
 
 declare let x10: [Box<number>, Box<string>, ...Box<boolean>[]];
@@ -147,6 +155,14 @@ declare type B = {
     b: string;
 };
 declare type T40 = Boxified<A | A[] | ReadonlyArray<A> | [A, B] | string | string[]>;
+declare type ReadWrite<T> = {
+    -readonly [P in keyof T]: T[P];
+};
+declare type T50 = Readonly<string[]>;
+declare type T51 = Readonly<[number, number]>;
+declare type T52 = Partial<Readonly<string[]>>;
+declare type T53 = Readonly<Partial<string[]>>;
+declare type T54 = ReadWrite<Required<T53>>;
 declare function unboxify<T>(x: Boxified<T>): T;
 declare let x10: [Box<number>, Box<string>, ...Box<boolean>[]];
 declare let y10: [number, string, ...boolean[]];
diff --git a/tests/baselines/reference/mappedTypesArraysTuples.symbols b/tests/baselines/reference/mappedTypesArraysTuples.symbols
index ffc7fe19e3f..48a3979585c 100644
--- a/tests/baselines/reference/mappedTypesArraysTuples.symbols
+++ b/tests/baselines/reference/mappedTypesArraysTuples.symbols
@@ -108,247 +108,279 @@ type T40 = Boxified<A | A[] | ReadonlyArray<A> | [A, B] | string | string[]>;
 >A : Symbol(A, Decl(mappedTypesArraysTuples.ts, 22, 39))
 >B : Symbol(B, Decl(mappedTypesArraysTuples.ts, 24, 23))
 
+type ReadWrite<T> = { -readonly [P in keyof T] : T[P] };
+>ReadWrite : Symbol(ReadWrite, Decl(mappedTypesArraysTuples.ts, 27, 77))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 29, 15))
+>P : Symbol(P, Decl(mappedTypesArraysTuples.ts, 29, 33))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 29, 15))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 29, 15))
+>P : Symbol(P, Decl(mappedTypesArraysTuples.ts, 29, 33))
+
+type T50 = Readonly<string[]>;
+>T50 : Symbol(T50, Decl(mappedTypesArraysTuples.ts, 29, 56))
+>Readonly : Symbol(Readonly, Decl(lib.es5.d.ts, --, --))
+
+type T51 = Readonly<[number, number]>;
+>T51 : Symbol(T51, Decl(mappedTypesArraysTuples.ts, 31, 30))
+>Readonly : Symbol(Readonly, Decl(lib.es5.d.ts, --, --))
+
+type T52 = Partial<Readonly<string[]>>;
+>T52 : Symbol(T52, Decl(mappedTypesArraysTuples.ts, 32, 38))
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>Readonly : Symbol(Readonly, Decl(lib.es5.d.ts, --, --))
+
+type T53 = Readonly<Partial<string[]>>;
+>T53 : Symbol(T53, Decl(mappedTypesArraysTuples.ts, 33, 39))
+>Readonly : Symbol(Readonly, Decl(lib.es5.d.ts, --, --))
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+
+type T54 = ReadWrite<Required<T53>>;
+>T54 : Symbol(T54, Decl(mappedTypesArraysTuples.ts, 34, 39))
+>ReadWrite : Symbol(ReadWrite, Decl(mappedTypesArraysTuples.ts, 27, 77))
+>Required : Symbol(Required, Decl(lib.es5.d.ts, --, --))
+>T53 : Symbol(T53, Decl(mappedTypesArraysTuples.ts, 33, 39))
+
 declare function unboxify<T>(x: Boxified<T>): T;
->unboxify : Symbol(unboxify, Decl(mappedTypesArraysTuples.ts, 27, 77))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 29, 26))
->x : Symbol(x, Decl(mappedTypesArraysTuples.ts, 29, 29))
+>unboxify : Symbol(unboxify, Decl(mappedTypesArraysTuples.ts, 35, 36))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 37, 26))
+>x : Symbol(x, Decl(mappedTypesArraysTuples.ts, 37, 29))
 >Boxified : Symbol(Boxified, Decl(mappedTypesArraysTuples.ts, 0, 27))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 29, 26))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 29, 26))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 37, 26))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 37, 26))
 
 declare let x10: [Box<number>, Box<string>, ...Box<boolean>[]];
->x10 : Symbol(x10, Decl(mappedTypesArraysTuples.ts, 31, 11))
+>x10 : Symbol(x10, Decl(mappedTypesArraysTuples.ts, 39, 11))
 >Box : Symbol(Box, Decl(mappedTypesArraysTuples.ts, 0, 0))
 >Box : Symbol(Box, Decl(mappedTypesArraysTuples.ts, 0, 0))
 >Box : Symbol(Box, Decl(mappedTypesArraysTuples.ts, 0, 0))
 
 let y10 = unboxify(x10);
->y10 : Symbol(y10, Decl(mappedTypesArraysTuples.ts, 32, 3))
->unboxify : Symbol(unboxify, Decl(mappedTypesArraysTuples.ts, 27, 77))
->x10 : Symbol(x10, Decl(mappedTypesArraysTuples.ts, 31, 11))
+>y10 : Symbol(y10, Decl(mappedTypesArraysTuples.ts, 40, 3))
+>unboxify : Symbol(unboxify, Decl(mappedTypesArraysTuples.ts, 35, 36))
+>x10 : Symbol(x10, Decl(mappedTypesArraysTuples.ts, 39, 11))
 
 declare let x11: Box<number>[];
->x11 : Symbol(x11, Decl(mappedTypesArraysTuples.ts, 34, 11))
+>x11 : Symbol(x11, Decl(mappedTypesArraysTuples.ts, 42, 11))
 >Box : Symbol(Box, Decl(mappedTypesArraysTuples.ts, 0, 0))
 
 let y11 = unboxify(x11);
->y11 : Symbol(y11, Decl(mappedTypesArraysTuples.ts, 35, 3))
->unboxify : Symbol(unboxify, Decl(mappedTypesArraysTuples.ts, 27, 77))
->x11 : Symbol(x11, Decl(mappedTypesArraysTuples.ts, 34, 11))
+>y11 : Symbol(y11, Decl(mappedTypesArraysTuples.ts, 43, 3))
+>unboxify : Symbol(unboxify, Decl(mappedTypesArraysTuples.ts, 35, 36))
+>x11 : Symbol(x11, Decl(mappedTypesArraysTuples.ts, 42, 11))
 
 declare let x12: { a: Box<number>, b: Box<string[]> };
->x12 : Symbol(x12, Decl(mappedTypesArraysTuples.ts, 37, 11))
->a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 37, 18))
+>x12 : Symbol(x12, Decl(mappedTypesArraysTuples.ts, 45, 11))
+>a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 45, 18))
 >Box : Symbol(Box, Decl(mappedTypesArraysTuples.ts, 0, 0))
->b : Symbol(b, Decl(mappedTypesArraysTuples.ts, 37, 34))
+>b : Symbol(b, Decl(mappedTypesArraysTuples.ts, 45, 34))
 >Box : Symbol(Box, Decl(mappedTypesArraysTuples.ts, 0, 0))
 
 let y12 = unboxify(x12);
->y12 : Symbol(y12, Decl(mappedTypesArraysTuples.ts, 38, 3))
->unboxify : Symbol(unboxify, Decl(mappedTypesArraysTuples.ts, 27, 77))
->x12 : Symbol(x12, Decl(mappedTypesArraysTuples.ts, 37, 11))
+>y12 : Symbol(y12, Decl(mappedTypesArraysTuples.ts, 46, 3))
+>unboxify : Symbol(unboxify, Decl(mappedTypesArraysTuples.ts, 35, 36))
+>x12 : Symbol(x12, Decl(mappedTypesArraysTuples.ts, 45, 11))
 
 declare function nonpartial<T>(x: Partial<T>): T;
->nonpartial : Symbol(nonpartial, Decl(mappedTypesArraysTuples.ts, 38, 24))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 40, 28))
->x : Symbol(x, Decl(mappedTypesArraysTuples.ts, 40, 31))
+>nonpartial : Symbol(nonpartial, Decl(mappedTypesArraysTuples.ts, 46, 24))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 48, 28))
+>x : Symbol(x, Decl(mappedTypesArraysTuples.ts, 48, 31))
 >Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 40, 28))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 40, 28))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 48, 28))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 48, 28))
 
 declare let x20: [number | undefined, string?, ...boolean[]];
->x20 : Symbol(x20, Decl(mappedTypesArraysTuples.ts, 42, 11))
+>x20 : Symbol(x20, Decl(mappedTypesArraysTuples.ts, 50, 11))
 
 let y20 = nonpartial(x20);
->y20 : Symbol(y20, Decl(mappedTypesArraysTuples.ts, 43, 3))
->nonpartial : Symbol(nonpartial, Decl(mappedTypesArraysTuples.ts, 38, 24))
->x20 : Symbol(x20, Decl(mappedTypesArraysTuples.ts, 42, 11))
+>y20 : Symbol(y20, Decl(mappedTypesArraysTuples.ts, 51, 3))
+>nonpartial : Symbol(nonpartial, Decl(mappedTypesArraysTuples.ts, 46, 24))
+>x20 : Symbol(x20, Decl(mappedTypesArraysTuples.ts, 50, 11))
 
 declare let x21: (number | undefined)[];
->x21 : Symbol(x21, Decl(mappedTypesArraysTuples.ts, 45, 11))
+>x21 : Symbol(x21, Decl(mappedTypesArraysTuples.ts, 53, 11))
 
 let y21 = nonpartial(x21);
->y21 : Symbol(y21, Decl(mappedTypesArraysTuples.ts, 46, 3))
->nonpartial : Symbol(nonpartial, Decl(mappedTypesArraysTuples.ts, 38, 24))
->x21 : Symbol(x21, Decl(mappedTypesArraysTuples.ts, 45, 11))
+>y21 : Symbol(y21, Decl(mappedTypesArraysTuples.ts, 54, 3))
+>nonpartial : Symbol(nonpartial, Decl(mappedTypesArraysTuples.ts, 46, 24))
+>x21 : Symbol(x21, Decl(mappedTypesArraysTuples.ts, 53, 11))
 
 declare let x22: { a: number | undefined, b?: string[] };
->x22 : Symbol(x22, Decl(mappedTypesArraysTuples.ts, 48, 11))
->a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 48, 18))
->b : Symbol(b, Decl(mappedTypesArraysTuples.ts, 48, 41))
+>x22 : Symbol(x22, Decl(mappedTypesArraysTuples.ts, 56, 11))
+>a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 56, 18))
+>b : Symbol(b, Decl(mappedTypesArraysTuples.ts, 56, 41))
 
 let y22 = nonpartial(x22);
->y22 : Symbol(y22, Decl(mappedTypesArraysTuples.ts, 49, 3))
->nonpartial : Symbol(nonpartial, Decl(mappedTypesArraysTuples.ts, 38, 24))
->x22 : Symbol(x22, Decl(mappedTypesArraysTuples.ts, 48, 11))
+>y22 : Symbol(y22, Decl(mappedTypesArraysTuples.ts, 57, 3))
+>nonpartial : Symbol(nonpartial, Decl(mappedTypesArraysTuples.ts, 46, 24))
+>x22 : Symbol(x22, Decl(mappedTypesArraysTuples.ts, 56, 11))
 
 type Awaited<T> = T extends PromiseLike<infer U> ? U : T;
->Awaited : Symbol(Awaited, Decl(mappedTypesArraysTuples.ts, 49, 26))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 51, 13))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 51, 13))
+>Awaited : Symbol(Awaited, Decl(mappedTypesArraysTuples.ts, 57, 26))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 59, 13))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 59, 13))
 >PromiseLike : Symbol(PromiseLike, Decl(lib.es5.d.ts, --, --))
->U : Symbol(U, Decl(mappedTypesArraysTuples.ts, 51, 45))
->U : Symbol(U, Decl(mappedTypesArraysTuples.ts, 51, 45))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 51, 13))
+>U : Symbol(U, Decl(mappedTypesArraysTuples.ts, 59, 45))
+>U : Symbol(U, Decl(mappedTypesArraysTuples.ts, 59, 45))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 59, 13))
 
 type Awaitified<T> = { [P in keyof T]: Awaited<T[P]> };
->Awaitified : Symbol(Awaitified, Decl(mappedTypesArraysTuples.ts, 51, 57))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 52, 16))
->P : Symbol(P, Decl(mappedTypesArraysTuples.ts, 52, 24))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 52, 16))
->Awaited : Symbol(Awaited, Decl(mappedTypesArraysTuples.ts, 49, 26))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 52, 16))
->P : Symbol(P, Decl(mappedTypesArraysTuples.ts, 52, 24))
+>Awaitified : Symbol(Awaitified, Decl(mappedTypesArraysTuples.ts, 59, 57))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 60, 16))
+>P : Symbol(P, Decl(mappedTypesArraysTuples.ts, 60, 24))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 60, 16))
+>Awaited : Symbol(Awaited, Decl(mappedTypesArraysTuples.ts, 57, 26))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 60, 16))
+>P : Symbol(P, Decl(mappedTypesArraysTuples.ts, 60, 24))
 
 declare function all<T extends any[]>(...values: T): Promise<Awaitified<T>>;
->all : Symbol(all, Decl(mappedTypesArraysTuples.ts, 52, 55))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 54, 21))
->values : Symbol(values, Decl(mappedTypesArraysTuples.ts, 54, 38))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 54, 21))
+>all : Symbol(all, Decl(mappedTypesArraysTuples.ts, 60, 55))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 62, 21))
+>values : Symbol(values, Decl(mappedTypesArraysTuples.ts, 62, 38))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 62, 21))
 >Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --))
->Awaitified : Symbol(Awaitified, Decl(mappedTypesArraysTuples.ts, 51, 57))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 54, 21))
+>Awaitified : Symbol(Awaitified, Decl(mappedTypesArraysTuples.ts, 59, 57))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 62, 21))
 
 function f1(a: number, b: Promise<number>, c: string[], d: Promise<string[]>) {
->f1 : Symbol(f1, Decl(mappedTypesArraysTuples.ts, 54, 76))
->a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 56, 12))
->b : Symbol(b, Decl(mappedTypesArraysTuples.ts, 56, 22))
+>f1 : Symbol(f1, Decl(mappedTypesArraysTuples.ts, 62, 76))
+>a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 64, 12))
+>b : Symbol(b, Decl(mappedTypesArraysTuples.ts, 64, 22))
 >Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --))
->c : Symbol(c, Decl(mappedTypesArraysTuples.ts, 56, 42))
->d : Symbol(d, Decl(mappedTypesArraysTuples.ts, 56, 55))
+>c : Symbol(c, Decl(mappedTypesArraysTuples.ts, 64, 42))
+>d : Symbol(d, Decl(mappedTypesArraysTuples.ts, 64, 55))
 >Promise : Symbol(Promise, Decl(lib.es5.d.ts, --, --))
 
     let x1 = all(a);
->x1 : Symbol(x1, Decl(mappedTypesArraysTuples.ts, 57, 7))
->all : Symbol(all, Decl(mappedTypesArraysTuples.ts, 52, 55))
->a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 56, 12))
+>x1 : Symbol(x1, Decl(mappedTypesArraysTuples.ts, 65, 7))
+>all : Symbol(all, Decl(mappedTypesArraysTuples.ts, 60, 55))
+>a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 64, 12))
 
     let x2 = all(a, b);
->x2 : Symbol(x2, Decl(mappedTypesArraysTuples.ts, 58, 7))
->all : Symbol(all, Decl(mappedTypesArraysTuples.ts, 52, 55))
->a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 56, 12))
->b : Symbol(b, Decl(mappedTypesArraysTuples.ts, 56, 22))
+>x2 : Symbol(x2, Decl(mappedTypesArraysTuples.ts, 66, 7))
+>all : Symbol(all, Decl(mappedTypesArraysTuples.ts, 60, 55))
+>a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 64, 12))
+>b : Symbol(b, Decl(mappedTypesArraysTuples.ts, 64, 22))
 
     let x3 = all(a, b, c);
->x3 : Symbol(x3, Decl(mappedTypesArraysTuples.ts, 59, 7))
->all : Symbol(all, Decl(mappedTypesArraysTuples.ts, 52, 55))
->a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 56, 12))
->b : Symbol(b, Decl(mappedTypesArraysTuples.ts, 56, 22))
->c : Symbol(c, Decl(mappedTypesArraysTuples.ts, 56, 42))
+>x3 : Symbol(x3, Decl(mappedTypesArraysTuples.ts, 67, 7))
+>all : Symbol(all, Decl(mappedTypesArraysTuples.ts, 60, 55))
+>a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 64, 12))
+>b : Symbol(b, Decl(mappedTypesArraysTuples.ts, 64, 22))
+>c : Symbol(c, Decl(mappedTypesArraysTuples.ts, 64, 42))
 
     let x4 = all(a, b, c, d);
->x4 : Symbol(x4, Decl(mappedTypesArraysTuples.ts, 60, 7))
->all : Symbol(all, Decl(mappedTypesArraysTuples.ts, 52, 55))
->a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 56, 12))
->b : Symbol(b, Decl(mappedTypesArraysTuples.ts, 56, 22))
->c : Symbol(c, Decl(mappedTypesArraysTuples.ts, 56, 42))
->d : Symbol(d, Decl(mappedTypesArraysTuples.ts, 56, 55))
+>x4 : Symbol(x4, Decl(mappedTypesArraysTuples.ts, 68, 7))
+>all : Symbol(all, Decl(mappedTypesArraysTuples.ts, 60, 55))
+>a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 64, 12))
+>b : Symbol(b, Decl(mappedTypesArraysTuples.ts, 64, 22))
+>c : Symbol(c, Decl(mappedTypesArraysTuples.ts, 64, 42))
+>d : Symbol(d, Decl(mappedTypesArraysTuples.ts, 64, 55))
 }
 
 function f2<T extends any[]>(a: Boxified<T>) {
->f2 : Symbol(f2, Decl(mappedTypesArraysTuples.ts, 61, 1))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 63, 12))
->a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 63, 29))
+>f2 : Symbol(f2, Decl(mappedTypesArraysTuples.ts, 69, 1))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 71, 12))
+>a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 71, 29))
 >Boxified : Symbol(Boxified, Decl(mappedTypesArraysTuples.ts, 0, 27))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 63, 12))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 71, 12))
 
     let x: Box<any> | undefined = a.pop();
->x : Symbol(x, Decl(mappedTypesArraysTuples.ts, 64, 7))
+>x : Symbol(x, Decl(mappedTypesArraysTuples.ts, 72, 7))
 >Box : Symbol(Box, Decl(mappedTypesArraysTuples.ts, 0, 0))
 >a.pop : Symbol(Array.pop, Decl(lib.es5.d.ts, --, --))
->a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 63, 29))
+>a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 71, 29))
 >pop : Symbol(Array.pop, Decl(lib.es5.d.ts, --, --))
 
     let y: Box<any>[] = a.concat(a);
->y : Symbol(y, Decl(mappedTypesArraysTuples.ts, 65, 7))
+>y : Symbol(y, Decl(mappedTypesArraysTuples.ts, 73, 7))
 >Box : Symbol(Box, Decl(mappedTypesArraysTuples.ts, 0, 0))
 >a.concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
->a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 63, 29))
+>a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 71, 29))
 >concat : Symbol(Array.concat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
->a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 63, 29))
+>a : Symbol(a, Decl(mappedTypesArraysTuples.ts, 71, 29))
 }
 
 // Repro from #26163
 
 type ElementType<T> = T extends Array<infer U> ? U : never;
->ElementType : Symbol(ElementType, Decl(mappedTypesArraysTuples.ts, 66, 1))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 70, 17))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 70, 17))
+>ElementType : Symbol(ElementType, Decl(mappedTypesArraysTuples.ts, 74, 1))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 78, 17))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 78, 17))
 >Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
->U : Symbol(U, Decl(mappedTypesArraysTuples.ts, 70, 43))
->U : Symbol(U, Decl(mappedTypesArraysTuples.ts, 70, 43))
+>U : Symbol(U, Decl(mappedTypesArraysTuples.ts, 78, 43))
+>U : Symbol(U, Decl(mappedTypesArraysTuples.ts, 78, 43))
 
 type Mapped<T> = { [K in keyof T]: T[K] };
->Mapped : Symbol(Mapped, Decl(mappedTypesArraysTuples.ts, 70, 59))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 71, 12))
->K : Symbol(K, Decl(mappedTypesArraysTuples.ts, 71, 20))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 71, 12))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 71, 12))
->K : Symbol(K, Decl(mappedTypesArraysTuples.ts, 71, 20))
+>Mapped : Symbol(Mapped, Decl(mappedTypesArraysTuples.ts, 78, 59))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 79, 12))
+>K : Symbol(K, Decl(mappedTypesArraysTuples.ts, 79, 20))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 79, 12))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 79, 12))
+>K : Symbol(K, Decl(mappedTypesArraysTuples.ts, 79, 20))
 
 type F<T> = ElementType<Mapped<T>>;
->F : Symbol(F, Decl(mappedTypesArraysTuples.ts, 71, 42))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 73, 7))
->ElementType : Symbol(ElementType, Decl(mappedTypesArraysTuples.ts, 66, 1))
->Mapped : Symbol(Mapped, Decl(mappedTypesArraysTuples.ts, 70, 59))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 73, 7))
+>F : Symbol(F, Decl(mappedTypesArraysTuples.ts, 79, 42))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 81, 7))
+>ElementType : Symbol(ElementType, Decl(mappedTypesArraysTuples.ts, 74, 1))
+>Mapped : Symbol(Mapped, Decl(mappedTypesArraysTuples.ts, 78, 59))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 81, 7))
 
 type R1 = F<[string, number, boolean]>;  // string | number | boolean
->R1 : Symbol(R1, Decl(mappedTypesArraysTuples.ts, 73, 35))
->F : Symbol(F, Decl(mappedTypesArraysTuples.ts, 71, 42))
+>R1 : Symbol(R1, Decl(mappedTypesArraysTuples.ts, 81, 35))
+>F : Symbol(F, Decl(mappedTypesArraysTuples.ts, 79, 42))
 
 type R2 = ElementType<Mapped<[string, number, boolean]>>;  // string | number | boolean
->R2 : Symbol(R2, Decl(mappedTypesArraysTuples.ts, 74, 39))
->ElementType : Symbol(ElementType, Decl(mappedTypesArraysTuples.ts, 66, 1))
->Mapped : Symbol(Mapped, Decl(mappedTypesArraysTuples.ts, 70, 59))
+>R2 : Symbol(R2, Decl(mappedTypesArraysTuples.ts, 82, 39))
+>ElementType : Symbol(ElementType, Decl(mappedTypesArraysTuples.ts, 74, 1))
+>Mapped : Symbol(Mapped, Decl(mappedTypesArraysTuples.ts, 78, 59))
 
 // Repro from #26163
 
 declare function acceptArray(arr: any[]): void;
->acceptArray : Symbol(acceptArray, Decl(mappedTypesArraysTuples.ts, 75, 57))
->arr : Symbol(arr, Decl(mappedTypesArraysTuples.ts, 79, 29))
+>acceptArray : Symbol(acceptArray, Decl(mappedTypesArraysTuples.ts, 83, 57))
+>arr : Symbol(arr, Decl(mappedTypesArraysTuples.ts, 87, 29))
 
 declare function mapArray<T extends any[]>(arr: T): Mapped<T>;
->mapArray : Symbol(mapArray, Decl(mappedTypesArraysTuples.ts, 79, 47))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 80, 26))
->arr : Symbol(arr, Decl(mappedTypesArraysTuples.ts, 80, 43))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 80, 26))
->Mapped : Symbol(Mapped, Decl(mappedTypesArraysTuples.ts, 70, 59))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 80, 26))
+>mapArray : Symbol(mapArray, Decl(mappedTypesArraysTuples.ts, 87, 47))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 88, 26))
+>arr : Symbol(arr, Decl(mappedTypesArraysTuples.ts, 88, 43))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 88, 26))
+>Mapped : Symbol(Mapped, Decl(mappedTypesArraysTuples.ts, 78, 59))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 88, 26))
 
 function acceptMappedArray<T extends any[]>(arr: T) {
->acceptMappedArray : Symbol(acceptMappedArray, Decl(mappedTypesArraysTuples.ts, 80, 62))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 81, 27))
->arr : Symbol(arr, Decl(mappedTypesArraysTuples.ts, 81, 44))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 81, 27))
+>acceptMappedArray : Symbol(acceptMappedArray, Decl(mappedTypesArraysTuples.ts, 88, 62))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 89, 27))
+>arr : Symbol(arr, Decl(mappedTypesArraysTuples.ts, 89, 44))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 89, 27))
 
     acceptArray(mapArray(arr));
->acceptArray : Symbol(acceptArray, Decl(mappedTypesArraysTuples.ts, 75, 57))
->mapArray : Symbol(mapArray, Decl(mappedTypesArraysTuples.ts, 79, 47))
->arr : Symbol(arr, Decl(mappedTypesArraysTuples.ts, 81, 44))
+>acceptArray : Symbol(acceptArray, Decl(mappedTypesArraysTuples.ts, 83, 57))
+>mapArray : Symbol(mapArray, Decl(mappedTypesArraysTuples.ts, 87, 47))
+>arr : Symbol(arr, Decl(mappedTypesArraysTuples.ts, 89, 44))
 }
 
 // Repro from #26163
 
 type Unconstrained<T> = ElementType<Mapped<T>>;
->Unconstrained : Symbol(Unconstrained, Decl(mappedTypesArraysTuples.ts, 83, 1))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 87, 19))
->ElementType : Symbol(ElementType, Decl(mappedTypesArraysTuples.ts, 66, 1))
->Mapped : Symbol(Mapped, Decl(mappedTypesArraysTuples.ts, 70, 59))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 87, 19))
+>Unconstrained : Symbol(Unconstrained, Decl(mappedTypesArraysTuples.ts, 91, 1))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 95, 19))
+>ElementType : Symbol(ElementType, Decl(mappedTypesArraysTuples.ts, 74, 1))
+>Mapped : Symbol(Mapped, Decl(mappedTypesArraysTuples.ts, 78, 59))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 95, 19))
 
 type T1 = Unconstrained<[string, number, boolean]>;  // string | number | boolean
->T1 : Symbol(T1, Decl(mappedTypesArraysTuples.ts, 87, 47))
->Unconstrained : Symbol(Unconstrained, Decl(mappedTypesArraysTuples.ts, 83, 1))
+>T1 : Symbol(T1, Decl(mappedTypesArraysTuples.ts, 95, 47))
+>Unconstrained : Symbol(Unconstrained, Decl(mappedTypesArraysTuples.ts, 91, 1))
 
 type Constrained<T extends any[]> = ElementType<Mapped<T>>;
->Constrained : Symbol(Constrained, Decl(mappedTypesArraysTuples.ts, 88, 51))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 90, 17))
->ElementType : Symbol(ElementType, Decl(mappedTypesArraysTuples.ts, 66, 1))
->Mapped : Symbol(Mapped, Decl(mappedTypesArraysTuples.ts, 70, 59))
->T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 90, 17))
+>Constrained : Symbol(Constrained, Decl(mappedTypesArraysTuples.ts, 96, 51))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 98, 17))
+>ElementType : Symbol(ElementType, Decl(mappedTypesArraysTuples.ts, 74, 1))
+>Mapped : Symbol(Mapped, Decl(mappedTypesArraysTuples.ts, 78, 59))
+>T : Symbol(T, Decl(mappedTypesArraysTuples.ts, 98, 17))
 
 type T2 = Constrained<[string, number, boolean]>;  // string | number | boolean
->T2 : Symbol(T2, Decl(mappedTypesArraysTuples.ts, 90, 59))
->Constrained : Symbol(Constrained, Decl(mappedTypesArraysTuples.ts, 88, 51))
+>T2 : Symbol(T2, Decl(mappedTypesArraysTuples.ts, 98, 59))
+>Constrained : Symbol(Constrained, Decl(mappedTypesArraysTuples.ts, 96, 51))
 
diff --git a/tests/baselines/reference/mappedTypesArraysTuples.types b/tests/baselines/reference/mappedTypesArraysTuples.types
index 98a79e8b600..6b43cd510fb 100644
--- a/tests/baselines/reference/mappedTypesArraysTuples.types
+++ b/tests/baselines/reference/mappedTypesArraysTuples.types
@@ -68,6 +68,24 @@ type B = { b: string };
 type T40 = Boxified<A | A[] | ReadonlyArray<A> | [A, B] | string | string[]>;
 >T40 : string | Box<string>[] | Boxified<A> | Box<A>[] | readonly Box<A>[] | [Box<A>, Box<B>]
 
+type ReadWrite<T> = { -readonly [P in keyof T] : T[P] };
+>ReadWrite : ReadWrite<T>
+
+type T50 = Readonly<string[]>;
+>T50 : readonly string[]
+
+type T51 = Readonly<[number, number]>;
+>T51 : readonly [number, number]
+
+type T52 = Partial<Readonly<string[]>>;
+>T52 : readonly (string | undefined)[]
+
+type T53 = Readonly<Partial<string[]>>;
+>T53 : readonly (string | undefined)[]
+
+type T54 = ReadWrite<Required<T53>>;
+>T54 : string[]
+
 declare function unboxify<T>(x: Boxified<T>): T;
 >unboxify : <T>(x: Boxified<T>) => T
 >x : Boxified<T>
diff --git a/tests/baselines/reference/readonlyArraysAndTuples.errors.txt b/tests/baselines/reference/readonlyArraysAndTuples.errors.txt
new file mode 100644
index 00000000000..dd973def9a2
--- /dev/null
+++ b/tests/baselines/reference/readonlyArraysAndTuples.errors.txt
@@ -0,0 +1,47 @@
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(10,5): error TS2740: Type 'readonly string[]' is missing the following properties from type 'string[]': pop, push, reverse, shift, and 3 more.
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(12,5): error TS2740: Type 'readonly [string, string]' is missing the following properties from type 'string[]': pop, push, reverse, shift, and 3 more.
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(16,5): error TS2739: Type 'string[]' is missing the following properties from type '[string, string]': 0, 1
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(17,5): error TS2740: Type 'readonly string[]' is missing the following properties from type '[string, string]': 0, 1, pop, push, and 5 more.
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(18,5): error TS2740: Type 'readonly [string, string]' is missing the following properties from type '[string, string]': pop, push, reverse, shift, and 3 more.
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(19,5): error TS2739: Type 'string[]' is missing the following properties from type 'readonly [string, string]': 0, 1
+tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts(20,5): error TS2739: Type 'readonly string[]' is missing the following properties from type 'readonly [string, string]': 0, 1
+
+
+==== tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts (7 errors) ====
+    type T10 = string[];
+    type T11 = Array<string>;
+    type T12 = readonly string[];
+    type T13 = ReadonlyArray<string>;
+    
+    type T20 = [number, number];
+    type T21 = readonly [number, number];
+    
+    function f1(ma: string[], ra: readonly string[], mt: [string, string], rt: readonly [string, string]) {
+        ma = ra;  // Error
+        ~~
+!!! error TS2740: Type 'readonly string[]' is missing the following properties from type 'string[]': pop, push, reverse, shift, and 3 more.
+        ma = mt;
+        ma = rt;  // Error
+        ~~
+!!! error TS2740: Type 'readonly [string, string]' is missing the following properties from type 'string[]': pop, push, reverse, shift, and 3 more.
+        ra = ma;
+        ra = mt;
+        ra = rt;
+        mt = ma;  // Error
+        ~~
+!!! error TS2739: Type 'string[]' is missing the following properties from type '[string, string]': 0, 1
+        mt = ra;  // Error
+        ~~
+!!! error TS2740: Type 'readonly string[]' is missing the following properties from type '[string, string]': 0, 1, pop, push, and 5 more.
+        mt = rt;  // Error
+        ~~
+!!! error TS2740: Type 'readonly [string, string]' is missing the following properties from type '[string, string]': pop, push, reverse, shift, and 3 more.
+        rt = ma;  // Error
+        ~~
+!!! error TS2739: Type 'string[]' is missing the following properties from type 'readonly [string, string]': 0, 1
+        rt = ra;  // Error
+        ~~
+!!! error TS2739: Type 'readonly string[]' is missing the following properties from type 'readonly [string, string]': 0, 1
+        rt = mt;
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/readonlyArraysAndTuples.js b/tests/baselines/reference/readonlyArraysAndTuples.js
new file mode 100644
index 00000000000..769ff504251
--- /dev/null
+++ b/tests/baselines/reference/readonlyArraysAndTuples.js
@@ -0,0 +1,41 @@
+//// [readonlyArraysAndTuples.ts]
+type T10 = string[];
+type T11 = Array<string>;
+type T12 = readonly string[];
+type T13 = ReadonlyArray<string>;
+
+type T20 = [number, number];
+type T21 = readonly [number, number];
+
+function f1(ma: string[], ra: readonly string[], mt: [string, string], rt: readonly [string, string]) {
+    ma = ra;  // Error
+    ma = mt;
+    ma = rt;  // Error
+    ra = ma;
+    ra = mt;
+    ra = rt;
+    mt = ma;  // Error
+    mt = ra;  // Error
+    mt = rt;  // Error
+    rt = ma;  // Error
+    rt = ra;  // Error
+    rt = mt;
+}
+
+
+//// [readonlyArraysAndTuples.js]
+"use strict";
+function f1(ma, ra, mt, rt) {
+    ma = ra; // Error
+    ma = mt;
+    ma = rt; // Error
+    ra = ma;
+    ra = mt;
+    ra = rt;
+    mt = ma; // Error
+    mt = ra; // Error
+    mt = rt; // Error
+    rt = ma; // Error
+    rt = ra; // Error
+    rt = mt;
+}
diff --git a/tests/baselines/reference/readonlyArraysAndTuples.symbols b/tests/baselines/reference/readonlyArraysAndTuples.symbols
new file mode 100644
index 00000000000..1d6c7dd1dfa
--- /dev/null
+++ b/tests/baselines/reference/readonlyArraysAndTuples.symbols
@@ -0,0 +1,77 @@
+=== tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts ===
+type T10 = string[];
+>T10 : Symbol(T10, Decl(readonlyArraysAndTuples.ts, 0, 0))
+
+type T11 = Array<string>;
+>T11 : Symbol(T11, Decl(readonlyArraysAndTuples.ts, 0, 20))
+>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+type T12 = readonly string[];
+>T12 : Symbol(T12, Decl(readonlyArraysAndTuples.ts, 1, 25))
+
+type T13 = ReadonlyArray<string>;
+>T13 : Symbol(T13, Decl(readonlyArraysAndTuples.ts, 2, 29))
+>ReadonlyArray : Symbol(ReadonlyArray, Decl(lib.es5.d.ts, --, --))
+
+type T20 = [number, number];
+>T20 : Symbol(T20, Decl(readonlyArraysAndTuples.ts, 3, 33))
+
+type T21 = readonly [number, number];
+>T21 : Symbol(T21, Decl(readonlyArraysAndTuples.ts, 5, 28))
+
+function f1(ma: string[], ra: readonly string[], mt: [string, string], rt: readonly [string, string]) {
+>f1 : Symbol(f1, Decl(readonlyArraysAndTuples.ts, 6, 37))
+>ma : Symbol(ma, Decl(readonlyArraysAndTuples.ts, 8, 12))
+>ra : Symbol(ra, Decl(readonlyArraysAndTuples.ts, 8, 25))
+>mt : Symbol(mt, Decl(readonlyArraysAndTuples.ts, 8, 48))
+>rt : Symbol(rt, Decl(readonlyArraysAndTuples.ts, 8, 70))
+
+    ma = ra;  // Error
+>ma : Symbol(ma, Decl(readonlyArraysAndTuples.ts, 8, 12))
+>ra : Symbol(ra, Decl(readonlyArraysAndTuples.ts, 8, 25))
+
+    ma = mt;
+>ma : Symbol(ma, Decl(readonlyArraysAndTuples.ts, 8, 12))
+>mt : Symbol(mt, Decl(readonlyArraysAndTuples.ts, 8, 48))
+
+    ma = rt;  // Error
+>ma : Symbol(ma, Decl(readonlyArraysAndTuples.ts, 8, 12))
+>rt : Symbol(rt, Decl(readonlyArraysAndTuples.ts, 8, 70))
+
+    ra = ma;
+>ra : Symbol(ra, Decl(readonlyArraysAndTuples.ts, 8, 25))
+>ma : Symbol(ma, Decl(readonlyArraysAndTuples.ts, 8, 12))
+
+    ra = mt;
+>ra : Symbol(ra, Decl(readonlyArraysAndTuples.ts, 8, 25))
+>mt : Symbol(mt, Decl(readonlyArraysAndTuples.ts, 8, 48))
+
+    ra = rt;
+>ra : Symbol(ra, Decl(readonlyArraysAndTuples.ts, 8, 25))
+>rt : Symbol(rt, Decl(readonlyArraysAndTuples.ts, 8, 70))
+
+    mt = ma;  // Error
+>mt : Symbol(mt, Decl(readonlyArraysAndTuples.ts, 8, 48))
+>ma : Symbol(ma, Decl(readonlyArraysAndTuples.ts, 8, 12))
+
+    mt = ra;  // Error
+>mt : Symbol(mt, Decl(readonlyArraysAndTuples.ts, 8, 48))
+>ra : Symbol(ra, Decl(readonlyArraysAndTuples.ts, 8, 25))
+
+    mt = rt;  // Error
+>mt : Symbol(mt, Decl(readonlyArraysAndTuples.ts, 8, 48))
+>rt : Symbol(rt, Decl(readonlyArraysAndTuples.ts, 8, 70))
+
+    rt = ma;  // Error
+>rt : Symbol(rt, Decl(readonlyArraysAndTuples.ts, 8, 70))
+>ma : Symbol(ma, Decl(readonlyArraysAndTuples.ts, 8, 12))
+
+    rt = ra;  // Error
+>rt : Symbol(rt, Decl(readonlyArraysAndTuples.ts, 8, 70))
+>ra : Symbol(ra, Decl(readonlyArraysAndTuples.ts, 8, 25))
+
+    rt = mt;
+>rt : Symbol(rt, Decl(readonlyArraysAndTuples.ts, 8, 70))
+>mt : Symbol(mt, Decl(readonlyArraysAndTuples.ts, 8, 48))
+}
+
diff --git a/tests/baselines/reference/readonlyArraysAndTuples.types b/tests/baselines/reference/readonlyArraysAndTuples.types
new file mode 100644
index 00000000000..a7917f5da2b
--- /dev/null
+++ b/tests/baselines/reference/readonlyArraysAndTuples.types
@@ -0,0 +1,87 @@
+=== tests/cases/conformance/types/tuple/readonlyArraysAndTuples.ts ===
+type T10 = string[];
+>T10 : string[]
+
+type T11 = Array<string>;
+>T11 : string[]
+
+type T12 = readonly string[];
+>T12 : readonly string[]
+
+type T13 = ReadonlyArray<string>;
+>T13 : readonly string[]
+
+type T20 = [number, number];
+>T20 : [number, number]
+
+type T21 = readonly [number, number];
+>T21 : readonly [number, number]
+
+function f1(ma: string[], ra: readonly string[], mt: [string, string], rt: readonly [string, string]) {
+>f1 : (ma: string[], ra: readonly string[], mt: [string, string], rt: readonly [string, string]) => void
+>ma : string[]
+>ra : readonly string[]
+>mt : [string, string]
+>rt : readonly [string, string]
+
+    ma = ra;  // Error
+>ma = ra : readonly string[]
+>ma : string[]
+>ra : readonly string[]
+
+    ma = mt;
+>ma = mt : [string, string]
+>ma : string[]
+>mt : [string, string]
+
+    ma = rt;  // Error
+>ma = rt : readonly [string, string]
+>ma : string[]
+>rt : readonly [string, string]
+
+    ra = ma;
+>ra = ma : string[]
+>ra : readonly string[]
+>ma : string[]
+
+    ra = mt;
+>ra = mt : [string, string]
+>ra : readonly string[]
+>mt : [string, string]
+
+    ra = rt;
+>ra = rt : readonly [string, string]
+>ra : readonly string[]
+>rt : readonly [string, string]
+
+    mt = ma;  // Error
+>mt = ma : string[]
+>mt : [string, string]
+>ma : string[]
+
+    mt = ra;  // Error
+>mt = ra : readonly string[]
+>mt : [string, string]
+>ra : readonly string[]
+
+    mt = rt;  // Error
+>mt = rt : readonly [string, string]
+>mt : [string, string]
+>rt : readonly [string, string]
+
+    rt = ma;  // Error
+>rt = ma : string[]
+>rt : readonly [string, string]
+>ma : string[]
+
+    rt = ra;  // Error
+>rt = ra : readonly string[]
+>rt : readonly [string, string]
+>ra : readonly string[]
+
+    rt = mt;
+>rt = mt : [string, string]
+>rt : readonly [string, string]
+>mt : [string, string]
+}
+