Constraint programming models solving

Hi
Can Mathematica solve mixed constraint programming models that include interval data for variables and different types of constraints?
Are there any examples of such constraints for Number theory tasks?
Like x^4+y^4+z^4=t^4 with conditions on x, y, z, t
Web versions to test.

There is FindInstance:


    FindInstance[x^4 + y^4 + z^4 == t^4 , {x, y, z, t}, PositiveIntegers]


    {{x -> 18796760, y -> 2682440, z -> 15365639, t -> 20615673}}

Minimize and Solveand a few other functions can also pop out AN answer.

If the problem is small enough, Solve with various constraints may do what you want.

Reduce can be useful for finding a possible algorithm to search for answers as well.

For deeper number theory functionality, it may be necessary to write your own algorithms.