prolog [ isGram3 union_d ] 6.
(*Intros Id_union_X_V1_f isGram_X_V1_R1_S1. Apply Id_union_X_V1_f. Apply union_d. Apply isGram3 with X R1; Assumption.*)
Qed.

Lemma Gim_egal : Gim = (Xim, (Vim, (Rim, Sim))).
unfold Sim, Rim, Gim3, Vim, Gim2, Xim in |- *.