(1) Just oneF cat is in the room. ⇒ ¬(n cats are in the room), for each number n > 1
(2) Only PatrickF is in the room. ⇒ ¬(x is in the room), for each relevant x
(3) Just oneF cat makes me happy. ⇒ any number of cats make me happy
(4) ??Only oneF cat makes me happy.
(30) Just oneF cat made me happy.
(31) Even just oneF cat made me happy.