pretty print fix

src/tea3/pretty_print.py

@@ -1,11 +1,11 @@
 def pretty_print(poly):
-    ring = poly.parent()
-
     R_terms = []
     r_terms = []
     x_terms = []
     mixed_terms = []
 
+    has_const = bool(poly.constant_coefficient())
+
     for monom in poly:
         vars_in_term = [str(v) for v in monom.variables()]
 
@@ -26,6 +26,9 @@ def pretty_print(poly):
 
     parts = []
 
+    if has_const:
+        parts.append("1")
+
     if R_terms:
         parts.append("f(Ri)")