Fix incorrect parenthesis

parse.lisp

@@ -108,26 +108,9 @@ proposition."))
     (open-paren most-positive-fixnum)
     (t nil)))
 
-(defun operator-argument-count (oper)
-  "Return the minimum number of arguments that OPER takes as the first value,
-and the maximum number (or nil for infinity) as a second value."
-  (case oper
-    (and (values 2 nil))
-    (or (values 2 nil))
-    (xor (values 2 nil))
-    (not (values 1 1))
-    (implies (values 2 2))
-    (converse (values 2 2))
-    (iff (values 2 2))
-    (nand (values 2 nil))
-    (nor (values 2 2))
-    (open-paren (values 0 0))
-    (t (error "unknown operator: ~S" oper))))
-
 (defun unary-p (oper)
   "Return whether OPER is a unary operator or not."
-  (when oper
-    (= 1 (operator-argument-count oper))))
+  (eq oper 'not))
 
 (defun interpret-operand (oper-str)
   "Return a symbol representing OPER-STR, or the string itself if it represents
@@ -267,7 +250,7 @@ found variables."
                    (error 'proposition-parse-error :message "no more operators"
                                                    :position pos
                                                    :proposition prop-str))
-                 (let ((oper-args (operator-argument-count oper))
+                 (let ((oper-args (if (unary-p oper) 1 2))
                        (cur-operands (list (pop operands))))
                    (when (not (car cur-operands))
                      (error 'proposition-parse-error