add_nb_set/3

Documentation
- Reference manual
  - The SWI-Prolog library
    - library(nb_set): Non-backtrackable set
- Packages

Availability::- use_module(library(nb_set)).(can be autoloaded)

add_nb_set(+Key, !Set, ?New)

If Key is not in Set and New is unified to true, Key is added to Set. If Key is in Set, New is unified to false. It can be used for many purposes:

`add_nb_set(+, +, false)`	Test membership
`add_nb_set(+, +, true)`	Succeed only if new member
`add_nb_set(+, +, Var)`	Succeed, binding `Var`