CMNT	 	on input: É ¥ val/bool/É
CMNT	 	output:  new val/É
CMNT	 	new val = -val   if bool = FALSE
CMNT	 	new val = val   if bool = TRUE
PRIM	Stack/Swap	É ¥ bool/val/É
BRFL	 	branch if FALSE (need to negate input)
	PRIM	Value/Negate	-val/É
BRTR