Definition nielim x a b c d e :=
ielim x a b c d e nil.

Lemma nielim_c x a b c d e :
{v[x]} = ({v[a]} ∨ {v[b]}) ∧({v[c]} ∨ {v[d]}) :> vect K ->
{e[nielim x a b c d e]} = {e[e]}.