| C.Var _ -> false
| C.Meta _ -> false
| C.Sort _ -> false
- | C.Implicit -> raise NotImplemented
+ | C.Implicit _ -> assert false
| C.Prod (_,s,t) -> (occur uri s) or (occur uri t)
| C.Cast (te,ty) -> (occur uri te)
| C.Lambda (_,s,t) -> (occur uri s) or (occur uri t) (* or false ?? *)