import proveit
# Prepare this notebook for defining the axioms of a theory:
%axioms_notebook # Keep this at the top following 'import proveit'.
from proveit import x, S
from proveit.logic import Equals, Forall, InSet, PowerSet, SubsetEq
%begin axioms
power_set_def = Forall((x, S), Equals(InSet(x, PowerSet(S)),
SubsetEq(x, S)))
%end axioms