export function testStack(a: number, b: number): number | undefined {
  // Implementa createStack con closure y úsalo aquí
  function createStack() {
    // Array privado aquí
    const arr = []
    return {
      push(value: number) {return arr.push(value)},
      pop(): number | undefined { return arr.pop(); },
      size(): number { return arr.length; },
    };
  }

  const stack = createStack();
  stack.push(a);
  stack.push(b);
  return stack.pop();
}