If someone is cooking downstairs, it will always cause the first floor to become smokey.
There are two kitchens in the house: the upstairs kitchen and the downstairs kitchen. When someone is cooking in the downstairs kitchen, the first floor becomes smokey unless the air conditioner is running. If the air conditioner is running and someone is cooking in the downstairs kitchen, all the smoke travels to the second floor.
∀x (Kitchen(x) → Up(x) ⊕ Down(x)) (Cook(downstairs) ∧ ¬Run(ac)) → Smokey(firstFloor) (Cook(downstairs) ∧ Run(ac)) → Smokey(secondFloor)