OptionalpreserveWhether the unfolded query counts a triple two solutions of the mapping body both produce once, the way the mapped graph - a set - does, rather than twice. Hugely costly: it deduplicates the whole body of every unfolded pattern, where the unfolding otherwise streams. Off by default, so turn it on only when the multiplicity of a solution is part of the answer you need.
What an unfolding may be configured with.