Eval_decomp = ->
	h = tos
	push(symbol(NIL))
	push(cadr(p1))
	Eval()
	push(caddr(p1))
	Eval()
	p1 = pop()
	if (p1 == symbol(NIL))
		guess()
	else
		push(p1)
	decomp()
	list(tos - h)

# returns constant expresions on the stack

decomp = ->
	save()

	p2 = pop()
	p1 = pop()

	# is the entire expression constant?

	if (Find(p1, p2) == 0)
		push(p1)
		#push(p1);	# may need later for pushing both +a, -a
		#negate()
		restore()
		return

	# sum?

	if (isadd(p1))
		decomp_sum()
		restore()
		return

	# product?

	if (car(p1) == symbol(MULTIPLY))
		decomp_product()
		restore()
		return

	# naive decomp if not sum or product

	p3 = cdr(p1)
	while (iscons(p3))
		push(car(p3))
		push(p2)
		decomp()
		p3 = cdr(p3)

	restore()

decomp_sum = ->
	h = 0

	# decomp terms involving x

	p3 = cdr(p1)

	while (iscons(p3))
		if (Find(car(p3), p2))
			push(car(p3))
			push(p2)
			decomp()
		p3 = cdr(p3)

	# add together all constant terms

	h = tos

	p3 = cdr(p1)

	while (iscons(p3))
		if (Find(car(p3), p2) == 0)
			push(car(p3))
		p3 = cdr(p3)

	if (tos - h)
		add_all(tos - h)
		p3 = pop()
		push(p3)
		push(p3)
		negate();	# need both +a, -a for some integrals

decomp_product = ->
	h = 0

	# decomp factors involving x

	p3 = cdr(p1)

	while (iscons(p3))
		if (Find(car(p3), p2))
			push(car(p3))
			push(p2)
			decomp()
		p3 = cdr(p3)

	# multiply together all constant factors

	h = tos

	p3 = cdr(p1)

	while (iscons(p3))
		if (Find(car(p3), p2) == 0)
			push(car(p3))
		p3 = cdr(p3)

	if (tos - h)
		multiply_all(tos - h)
		#p3 = pop();	# may need later for pushing both +a, -a
		#push(p3)
		#push(p3)
		#negate()