###
Remove terms that involve a given symbol or expression. For example...

  filter(x^2 + x + 1, x)    =>  1

  filter(x^2 + x + 1, x^2)  =>  x + 1
###



Eval_filter = ->
  p1 = cdr(p1)
  push(car(p1))
  Eval()
  p1 = cdr(p1)
  while (iscons(p1))
    push(car(p1))
    Eval()
    filter()
    p1 = cdr(p1)

###
 For example...

  push(F)
  push(X)
  filter()
  F = pop()
###

filter = ->
  save()
  p2 = pop()
  p1 = pop()
  filter_main()
  restore()

filter_main = ->
  if (car(p1) == symbol(ADD))
    filter_sum()
  else if (istensor(p1))
    filter_tensor()
  else if (Find(p1, p2))
    push_integer(0)
  else
    push(p1)

filter_sum = ->
  push_integer(0)
  p1 = cdr(p1)
  while (iscons(p1))
    push(car(p1))
    push(p2)
    filter()
    add()
    p1 = cdr(p1)

filter_tensor = ->
  i = 0
  n = 0
  n = p1.tensor.nelem
  p3 = alloc_tensor(n)
  p3.tensor.ndim = p1.tensor.ndim
  for i in [0...p1.tensor.ndim]
    p3.tensor.dim[i] = p1.tensor.dim[i]
  for i in [0...n]
    push(p1.tensor.elem[i])
    push(p2)
    filter()
    p3.tensor.elem[i] = pop()
  push(p3)