# list.py

# This is not a test program but is required for the test programs to run using
# Python. It defines several functions on lists.

def cons (head, tail) :
  return [head] + tail

def head (list) :
  return list [0]

def tail (list) :
  return list [1 : len (list)]

# no longer needed 

def isNil (list) :
  return len (list) == 0