Plaster

(defun xnor-gate(a b) (cond ((and (= a 0) (= b 0)) 1) ((and (= a 0) (= b 1)) 0) ((and (= a 1) (= b 0)) 0) ((and (= a 1) (= b 1)) 1) (t (error 'on-exception%logic-error :message *e-logic-error*))))