MODIFIED: base library(nb_set) on hash tables rather than (unbalanced) trees.  Tests indicate that using non-backtrackable primitives to implement balancing trees comes at a quite high linear overhead.  Hash tables are simpler.
MODIFIED: base library(nb_set) on hash tables rather than (unbalanced)
trees.  Tests indicate that using non-backtrackable primitives to implement
balancing trees comes at a quite high linear overhead.  Hash tables are
simpler.

Adding new terms to the set is now based on =@=/2 rather than ==/2.  ==/2
is rather meaningless as the term is compared with a _copy_ and therefore
variables never compare equal.

edechter/swipl-devel,edechter/swipl-devel,edechter/swipl-devel,edechter/swipl-devel,edechter/swipl-devel