In reply to om30:
You need to explain the “but” operator in your description. I think you mean
a,b,c has a value between 0 to 7, additionally a,b,c must have unique values. The constraint would look like:
constraint a1 { a inside { [00:07] }; }
constraint b1 { b inside { [00:07] }; }
constraint c1 { c inside { [00:07] }; }
constraint.u1 { unique {a,b,c}; }