[cenamus]

Is there a similarly short/simple solution not using all of the built ins? Haven't worked with prolog in a while but should be easy enough with primitives (albeit with more duplication)?

[crustycoder]

Well no, not really. The whole point is to use the appropriate tool for the task at hand. In this case it's the CLP(FD) library, https://www.swi-prolog.org/pldoc/man?section=clpfd