text: var permuter = require('./index');
  
  permuter(
    ["a", "b"],
    [1, 2],
    function(letter, number) {
      console.log(letter.value, number.value);
    }
  )
  
  console.log("\n");
  
  permuter(
    [1, 2, 5, 10], // Number
    [10, 4], // xFactor
    function applySomeReasoning(number, xFactor) {
      return number.value*2 == xFactor.value;
    },
    "words", ["a", "bo"],
    "$words", // Letter
    function(number, xFactor, word, letter) {
      console.log(word.value, letter.value, number.value, xFactor.value);
    }
  )
  