Cryptoanalysis solver

   4.  Here's a cryptarithmetic problem published in 1933 in a journal
       called "Sphinx":

           S E P T E M B R E
         - E R B M E T P E S
         -------------------
           M P P B R P S S M

        Use generate-and-test.  An appropriate query would be of the form:

         ?- crypto(S,E,P,T,M,B,R).

        which would return assignments for S,E,P,etc that make the math correct.

        Make sure you never let S=E, or P=T, etc... all of the
        distinct letters have to stand for distinct digits.

        It might run slowly!


crypto(S,E,P,T,M,B,R) :-
  % Every letter must be a valid digit.
  digit(S), digit(E), digit(P), digit(T), digit(M), digit(B), digit(R),
  % No digit can equal any other digit.
  S \= E, S \= P, S \= T, S \= M, S \= B, S \= R,
          E \= P, E \= T, E \= M, E \= B, E \= R,
                  P \= T, P \= M, P \= B, P \= R,
                          T \= M, T \= B, T \= R,
                                  M \= B, M \= R,
                                          B \= R,
  Minuend    is S*10^8 + E*10^7 + P*10^6 + T*10^5 + E*10^4 + M*10^3 + B*10^2 + R*10 + E,
  Subtrahend is E*10^8 + R*10^7 + B*10^6 + M*10^5 + E*10^4 + T*10^3 + P*10^2 + E*10 + S,
  Difference is Minuend - Subtrahend,
  Expected   is M*10^8 + P*10^7 + P*10^6 + B*10^5 + R*10^4 + P*10^3 + S*10^2 + S*10 + M,
  Difference = Expected.