#h #G #L #V #U1
elim (cpr_subst h G (L.ⓓV) U1 … 0) [|*: /2 width=4 by drops_refl/ ] #U2 #T2 #HU12 #HTU2
elim (tweq_dec U1 U2) [ #HpU12 | -HTU2 #HnU12 ]
#h #G #L #V #U1
elim (cpr_subst h G (L.ⓓV) U1 … 0) [|*: /2 width=4 by drops_refl/ ] #U2 #T2 #HU12 #HTU2
elim (tweq_dec U1 U2) [ #HpU12 | -HTU2 #HnU12 ]