I think that dot is a little 2. Looks like the heat equation to me, partially obscured by a pawn and a king.
No, it's two partial derivatives, whose dependent variables are camoflagued by two pawns.
An engineer, a physicist, and a mathematician were on a train heading north, and had just crossed the border into Scotland.
- The engineer looked out of the window and said "Look! Scottish sheep are black!"
- The physicist said, "No, no. Some Scottish sheep are black."
- The mathematician looked irritated. "There is at least one field, containing at least one sheep, of which at least one side is black."
- The statistician : "It's not significant. We only know there's one black sheep"
- The computer scientist : "Oh, no! A special case!"