[cLeEOGPw]

> those three statements encapsulate the entire source code required to perform a sort.

It is calling the resolver system though and all the accompanying functions that actually do the sorting.

Not sure what is your definition of "source code", but I'm pretty sure nobody counts external library function implementations as source code for the program. Same as you don't count OS kernel as part of your program's source code.

[rapala]

Yes, but the resolver is not specific to sorting. The runtime of Prolog contains no list sorting code. (Or if it does, it does so as an optimization.)