bagof(+Template, +Generator, -Set)
setof/3 except that the list (or alternative lists)
returned will not be ordered, and may contain duplicates. This
relaxation saves time and space in execution.
callable, must be nonvar
A goal to be proved as if by
list of term, non-empty set
Call errors (see ref-sem-exc).
findall/3 for examples that illustrate
the differences among