SWI-Prolog -- term_singletons/2

Documentation
- Reference manual
  - Built-in Predicates
    - Analysing and Constructing Terms
- Packages

Availability:built-in

term_singletons(+Term, -List)

Unify List with a list of variables, each sharing with a variable that appears only once in Term.^{bugIn
the current implementation Term must be acyclic. If not, a representation_error
is raised.} Note that, if a variable appears in a shared subterm, it is not considered singleton. Thus, A is not a singleton in the example below. See also the singleton option of numbervars/4.


?- S = a(A), term_singletons(t(S,S), L).
L = [].