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Formalizing Stratagems

It is stated in the Lemmings manual, and I observed it many times, that when a bridge builder bumps its head on a ceiling, it reverses course. An ordinary walker keeps going. To me this was an annoyance. It meant that to be able to reflect walkers, it was necessary to start bridge building several times. Recently, I found a use for the phenomenon, doubtless a use intended by the game designers. If we catch the ex-builder just after it has reversed, it will build a bridge in the opposite direction and will not be followed by other lemmings. This sometimes permits building a ladder of bridges without other lemmings falling off the partial bridges. After the builder has reached the destination the gaps can be closed, and the mob will follow.

I thought of the stratagem while away from the game.

The possibility of the stratagem is implied by previously known lemming physics. However,

  1. The stratagem is formulatable in natural language and in logic and can be communicated from one person to another. We need to figure out how to express such stratagems formally.
  2. It is not obvious how a program could be made to search for such stratagems.

John McCarthy
Mon Mar 2 16:21:50 PDT 1998