compare_si/3 missing

[UWN]

Still not in library(si), its definition is difficult in the presence of rational trees. A direct extension of the lexical ordering to rational trees does not exist. But it should be handled somehow.

[bakaq]

Could it throw an error in the case of rational trees?

[UWN]

Think of something along setof(t, G_0, _), does it make sense to produce here an error? The intention is clearly to eliminate redundant solutions.