import proveit
from proveit import x, A, B
from proveit.numbers import zero, Integer, Natural
from proveit.numbers.number_sets.natural_numbers import zero_in_nats
from proveit.numbers.number_sets.integers import nat_within_int
theory = proveit.Theory() # the theorem's theory
%proving zero_is_int
zero_in_nats
nat_within_int
%qed