Set Bullet Behavior "Strict Subproofs".
Opaque upto.

Lemma make_shares_sub : forall i lasts shs sh0 sh1 sh2 (Hlen : Zlength shs >= Zlength lasts)
(Hsh1 : sepalg_list.list_join sh0 shs sh1) (Hsh2 : sepalg_list.list_join sh0 (make_shares shs lasts i) sh2),
sepalg.join_sub sh2 sh1.