Comedy = Tragedy + Time
This is meant to suggest that a tragedy, once not so fresh in everyone's memory, will be suitable material for a joke. However, this equation also suggests something else; that you don't need much time to have passed at all, provided you had a colossal enough tragedy.
Seeing as that doesn't seem to be true, there has to be a more accurate generalization. A better formulation could be:
Comedy = Time / Tragedy
In this way we retain the comedy-boosting properties of time, without allowing a huge tragedy to positively affect the comedy factor. And the bigger the tragedy, the more time has to pass in order to reach maximum comedy levels.
However, this still leaves the definition of comedy stubbornly dependent on some sort of tragedy. If there's no tragedy at all, comedy will be undefined. Hopefully this drawback will be addressed by future developments in advanced comedy theory.