Cosmetics

Signed-off-by: Daniel Borchmann <daniel.borchmann@mailbox.tu-dresden.de>
Add «close-under-implications-1»

This function implements one application of a set of implications
to a given set, and might be useful if it is known that a set of
implications is direct

Signed-off-by: Daniel Borchmann <daniel.borchmann@mailbox.tu-dresden.de>