Chapter 6.2 add a reverse/4 solution and compare it to reverse/3 that we have till now in the lpn examples

[Wisermans]

Following my question on SWI Prolog Discourse, i would find it useful to update chapter 6.2 with reverse/4 and the comparison with reverse/3 as it is a good way to improve coding with a better understanding of how it works under the hood.