DONALD + GERALD = ROBERT
One solution is to add more variables to the problem
Variables C1, C2, C3, C4, C5
- Ci represents carry from previous column i
- DCi = {0,1}
- Now we can express more constraints
- D + D = 10*C1 + T
- C1 + L + L = 10*C2 + R
- C2 + A + A = 10*C3 + E
- C3 + N + R = 10*C4 + B
- C4 + O + E = 10*C5 + O
- C5 + D + G = R