split

func split(piv, str : List+String) -> (List+String)*(List+String)
  post result = Undefined or str = result(1) + piv + result(2)

Splits the given list or string around the pivot and returns the resulting prefix and suffix. For example:

  split(` and ' `prefix and suffix') = [`prefix' `suffix']
  split([1] [1 2 1 2]) = [[] [2 1 2]]
  split(`c' `abc') = [`ab' `']
  split(`x' `abc') = Undefined