% Specification of the railroad crossing example from M. Kanovich, M. Okada,
% and A. Scedrov, "Specifying Real-Time Finite-State Systems in Linear Logic".
% Backward chaining.
% Date: 7 July  1998
% Author: Iliano Cervesato

Backward chaining:

+ final values are available (no tricks)

- the specifications needs to be massaged quite a bit
- very inefficient (when read backwards, the given rules are extremely
  non-deterministic)