see dependencies
import proveit
from proveit import defaults
from proveit import x, y, A, B, C, Px
from proveit.logic import And, Equals, Forall, Implies, SubsetEq
from proveit.logic.equality import sub_right_side_into
from proveit.logic.sets.inclusion import subset_eq_def
from proveit.logic.sets.inclusion import subset_eq_reflexive
%proving subset_eq_via_equality
subset_eq_reflexive
subset_eq_reflexive_spec = subset_eq_reflexive.instantiate()
sub_right_side_into
sub_right_side_into.instantiate({Px:SubsetEq(A, x), x:A, y:B}, assumptions=[Equals(A, B)])
%qed