Conversely, what if you really need a Prolog system or indeed any general purpose programming language, but only have an interface to a more limited solver? I f

Conversely, what if you really need a Prolog system or indeed any general purpose programming language, but only have an interface to a more limited solver? I find this even more constrained. As technology progresses, interfaces to other solvers that appear from time to time become available in Prolog systems if enough users demand it. For many cases, a Prolog system is already more than sufficient on its own, and is far more flexible than specialized tools which can still be provided as add-ons to Prolog. It is straight-forward to use only a specific subset of Prolog, if that is all you need. In contrast, it is generally impossible to use basic features of Prolog, such as backtracking and logical variables, in more specialized tools and solvers.