text: function difference(a, b) {
    const result = new Set(a)
  
    for (const item of b) {
      if (a.has(item)) {
        result.delete(item)
      }
    }
  
    return result
  }
  
  function union(a, b) {
    const result = new Set(a)
  
    for (const item of b) {
      result.add(item)
    }
  
    return result
  }
  
  module.exports = {
    difference,
    union,
  }
  