def redundanceFreeRot13 = {
  it.inject(''){ result, c ->
    result + (char)((c as char) + rotCount(c))
  }
}

def rotCount(c) {
  if(c in upperAndLowerCase('a'..'m')) return  13
  if(c in upperAndLowerCase('n'..'z')) return -13
  0
}

def upperAndLowerCase(characters) {
  characters*.toUpperCase() + characters*.toLowerCase()
}