text: // Set that counts
  module.exports = class CountedSet {
    constructor() {
      // because you can't simply extend Builtins yet
      this.map = new Map();
    }
    keys() {
      return [...this.map.keys()];
    }
    has(value) {
      return this.map.has(value);
    }
    add(value) {
      if (!this.has(value)) {
        this.map.set(value, 0);
      }
      this.map.set(value, this.map.get(value) + 1);
    }
    delete(value) {
      if (!this.has(value)) return;
      const count = this.map.get(value);
      if (count <= 1) {
        this.map.delete(value);
      } else {
        this.map.set(value, count - 1);
      }
    }
  };
  