const r1 = [1, 2, 3].myFilter((v) => v < 2);
// Signature '(v: number): boolean' must be a type predicate.
const r2 = [1, 2, 3].myFilter((v, i, a) => {});
// Signature '(v: number, i: number, a: number[]): void' must be a type predicate.
const r3 = ['1', 2, '3'].myFilter((v) => typeof v === 'string');
// Signature '(v: number): boolean' must be a type predicate.
const r4 = [{ num: 1 }, { num: 2 }, { num: 3 }].myFilter(function(v) {
  return v.num % 2;
});
// Signature '(v: { num: number; }): number' must be a type predicate.

interface Array<T> {
  myFilter<S extends T>(callback: (v: T, i: number, a: T[]) => v is S, thisArg?: any): S[];
}