Donald + Gerald = Robert

• We can write one long constraint for the sum:

  • 100000*D + 10000*O + 1000*N + 100*A+ 10*L + D + 100000*G + 10000*E + 1000*R + 100*A+ 10*L + D = 100000*R + 10000*O + 1000*B + 100*E+ 10*R + T

• But what about the difference between variables?

  • Could write D =/= O, D=/=N, … B =/= T
  • Or express it as a single constraint on all variables
  • AllDifferent(D,O,N,A,L,G,E,R,B,T)

• These two constraints

  • express the problem precisely
  • both involve all the 10 variables in the problem

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