An example to expand on Martin's second paragraph above: once the tag 'propositional logic' (PL) is synonymised as 'first-order logic' (FOL) with no merger done, any onsite search for the tag 'propositional logic' no longer returns any result from set of existing posts that are tagged-PL-but-not-tagged-FOL. Thus, I feel that synonimising without merging tags is by design a transitory/interim/provisional state, and that (with consensus) either a full merger or a desynonymisation ought to be the end-point. — ryang 16 hours ago