member of list

11   *  33 *  ...22 0
100 101 102 103 104 105

member x, L
  if head(L) == x return yes
  while tail(L) != 0
    if head(L) == x return yes
    L = tail(L)
  return no

member2(x, L)
  while L != 0
    if head(L) == x return yes
    L = tail(L)
  return no

memberrec(x, L)
  if head(L) == x return yes
  if tail(L) == 0 return no
  return memberrec(x, tail(L))
