example of "sameness" in the context of nested immutable data (> TS 3.4 needed @see https://devblogs.microsoft.com/typescript/announcing-typescript-3-4/#improvements-for-readonlyarray-and-readonly-tuples)

arePairsOfPairsEqual.immutable.ts

type Pair<T> = readonly [T, T];
type NumberPair = Pair<number>;
type PairOfNumberPairs = Pair<NumberPair>;

const areNumbersEqual = (a: number, b: number) => a === b;
const arePairsEqual = <T>(
  a: Pair<T>,
  b: Pair<T>,
  isEqual: (a: T, b: T) => boolean
) => isEqual(a[0], b[0]) && isEqual(a[1], b[1]);

const areNumberPairsEqual = (a: NumberPair, b: NumberPair) =>
  arePairsEqual(a, b, areNumbersEqual);

const arePairsOfNumberPairsEqual = (
  a: PairOfNumberPairs,
  b: PairOfNumberPairs
) => arePairsEqual(a, b, areNumberPairsEqual);

arePairsOfNumberPairsEqual([[1, 2], [3, 4]], [[1, 2], [3, 4]]); // true
arePairsOfNumberPairsEqual([[1, 2], [3, 4]], [[1, 2], [3, 5]]); // false