[Dingle-Dingle]

Three mathematicians were walking down to the railway station one day, deep in conversation about mathematics.
They were so absorbed in what they were talking about that as they approached the station, they failed to hear the announcement that the train was about to leave.
However they did notice when the train started to pull away from the platform. Alarmed, they started to run after the train, and eventually two of them managed to scramble on board.
A station porter noticed the remaining man looking glum. "Never mind", he said, "Two out of three isn't bad."
"But you don't understand," replied the mathematician, "they only came to see me off."

DD