Add trig expression copying

larcs.org

@@ -589,10 +589,14 @@ Trigonemtric functions are also a bit weird -- as given a "normal" trig function
 
   (defmethod eqal ((expression-a <trig>) (expression-b <trig>))
     (and (equal (type-of expression-a)
-               (type-of expression-b))
+              (type-of expression-b))
        (eqal (expression expression-a)
              (expression expression-b))))
 
+  (defmethod copy-expression ((expression <trig>))
+    (make-instance (type-of expression)
+                   :expression (copy-expression (slot-value expression 'expression))))
+
   @export
   (defclass <sin> (<trig>) ())