I agree that the documentation needs improvement.It needs to be defined what kind of relation opCmp is meant to model.
If it's concept is a partial order, opEquals cannot be inferred.If it's concept is a strict weak ordering [1, 2], which is required for sorting, opEqual can be inferred.
[1] https://www.sgi.com/tech/stl/StrictWeakOrdering.html[2] https://en.wikipedia.org/wiki/Weak_ordering#Strict_weak_orderings
