(fanin-litp x aignet) checks whether a literal is appropriate as a fanin to another node.
Executable version of aignet-litp. True iff the literal's ID is in bounds and belongs to a non-output, non-next-state node.
Macro: fanin-litp
(defmacro fanin-litp (x aignet) (cons 'id-existsp (cons (cons 'lit->var (cons x 'nil)) (cons aignet 'nil))))
