*)
(* it seems unbelivable, but it works! *)
-notation > "≔ (list0 ( (list1 (ident x) sep , ) opt (: T) ) sep ,) opt (; (list1 (ident U ≟ term 90 V ) sep ,)) ⊢ term 19 Px ≡ term 19 Py"
+notation > "≔ (list0 ( (list1 (ident x) sep , ) opt (: T) ) sep ,) opt (; (list1 (ident U ≟ term 19 V ) sep ,)) ⊢ term 19 Px ≡ term 19 Py"
with precedence 90
for @{ ${ fold right
@{ ${ default