Deduction substituting both sides of an implication. (Contributed by Wolf Lammen, 24-Nov-2022.) Revise [df-sb]. (Revised by Steven Nguyen, 9-Jul-2023.)
Deduction substituting both sides of an implication. (Contributed by Wolf Lammen, 24-Nov-2022.) Revise [df-sb]. (Revised by Steven Nguyen, 9-Jul-2023.)