Q.MATCH_ASSUM_ABBREV_TAC : term quotation -> tactic
Introduces abbreviations by matching a pattern against an assumption.
When applied to the goal (asl, w), the tactic Q.MATCH_ASSUM_ABBREV_TAC q parses the quotation q in the context of the goal, producing a term to use as a pattern. The tactic then attempts a (first order) match of the pattern against each term in asl, stopping on the first matching assumption a. Variables that occur in both the pattern and the goal are treated as “local constants”, and will not acquire instantiations.

For each variable v in the pattern that has not been treated as a local constant, there will be an instantiation term t, such that the substitution pattern[v1 |-> t1, v2 |-> t2, ...] produces a. The effect of the tactic is to then perform abbreviations in the goal, replacing each t with the corresponding v, and adding assumptions of the form Abbrev(v = t) to the goal.

MATCH_ABBREV_TAC fails if the pattern provided does not match any assumption, or if variables from the goal are used in the pattern in ways that make the pattern fail to type-check.
This tactic improves on the following tedious workflow: Q.PAT_ASSUM pat MP_TAC, Q.MATCH_ABBREV_TAC `pat ==> X`, Q.UNABBREV_TAC `X`, STRIP_TAC.
HOL  Kananaskis-14