simplify # trees: Catalan trees -> Wedderburn–Etherington trees

stack.c

@@ -107,6 +107,10 @@ int *push_stack(stack, val)
     int size=stack->size;
     int *pelt=stack->stack+stack->last;
 
+#ifdef DEBUG_STACK
+    printf("push_stack(%d): last=%d size=%d\n", val, stack->last, stack->size);
+#endif
+
     if (pos >= size) {
         fprintf(stderr, "stack overflow: size=%d last=%d\n", size, pos);
         return NULL;