import proveit
from proveit import defaults
from proveit import A, C
from proveit.logic import in_bool, Implies
from proveit.logic.booleans import unfold_is_bool
theory = proveit.Theory() # the theorem's theory
%proving from_excluded_middle
defaults.assumptions = from_excluded_middle.all_conditions()
unfold_is_bool
A_or_not_a = unfold_is_bool.instantiate({A:A})
Ctruth = A_or_not_a.derive_via_dilemma(C)
%qed