The problem is to implement three constraints, `and`

, `or`

and `xor`

in CHRs and, as a separate exercise, in Propia.
The constraints are specified as follows:
All boolean variables have domain {0,1}: 0 for ’false’ and 1
for ’true’.

and(X,Y,Z) =def (X & Y) = Z

or(X,Y,Z) =def (X or Y) = Z

xor(X,Y,Z) =def ((X & -Y) or (-X & Y)) = Z

Suppose your constraints are called
`cons_and`

, `cons_or`

and `cons_xor`

Now write enter the following procedure:

full_adder(I1,I2,I3,O1,O2) :- cons_xor(I1,I2,X1), cons_and(I1,I2,Y1), cons_xor(X1,I3,O1), cons_and(I3,X1,Y2), cons_or(Y1,Y2,O2). |

The problem is solved if you enter the query:

?- full_adder(I1,I2,0,O1,1).

and get the correct answer.

Note: you are not allowed to load the ic library nor to use search and backtracking!