for ,n-prev = (when ,node-var (node-prev ,node-var))
and ,lvar = (when (and ,node-var (valued-node-p ,node-var))
(node-lvar ,node-var))
for ,n-prev = (when ,node-var (node-prev ,node-var))
and ,lvar = (when (and ,node-var (valued-node-p ,node-var))
(node-lvar ,node-var))