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function mutation(arr) {
  var arr1 = arr[1].toLowerCase();
  var arr2 = arr[0].toLowerCase();
  
  for (var i = 0; i < arr1.length; i++) {
    if (arr2.indexOf(arr1[i]) < 0) 
      return false;
    }
  
  return true;
     
}

mutation(["hello", "hey"]);