Makes a mapping denote a set of triples rather than a bag, by deduplicating its body over the head's
own variables.
Those variables are the triple the head constructs, the head being injective in them, so deduplicating
them is deduplicating the triples the mapping produces - including a triple two merged mappings both
produce, the merged head being the three variables every branch binds. It is hugely costly: the
whole body of every unfolded pattern is materialised and sorted, where the unfolding otherwise streams.
Makes a mapping denote a set of triples rather than a bag, by deduplicating its body over the head's own variables.
Those variables are the triple the head constructs, the head being injective in them, so deduplicating them is deduplicating the triples the mapping produces - including a triple two merged mappings both produce, the merged head being the three variables every branch binds. It is hugely costly: the whole body of every unfolded pattern is materialised and sorted, where the unfolding otherwise streams.