The "false branch" of a UBDD.
(qcdr x) returns the false branch of the UBDD x.
For a compound UBDD, i.e., a . b), we simply return b. But for the atomic UBDDs t and nil, which represent the constant functions t and nil, this is the identity function.
Function: qcdr$inline
(defun qcdr$inline (x) (declare (xargs :guard t)) (if (consp x) (cdr x) x))
