| C.Cast (te,ty) -> C.Cast (aux k te, aux k ty)
| C.Prod (n,s,t) -> C.Prod (n, aux k s, aux (k+1) t)
| C.Lambda (n,s,t) -> C.Lambda (n, aux k s, aux (k+1) t)
| C.Cast (te,ty) -> C.Cast (aux k te, aux k ty)
| C.Prod (n,s,t) -> C.Prod (n, aux k s, aux (k+1) t)
| C.Lambda (n,s,t) -> C.Lambda (n, aux k s, aux (k+1) t)