Q.UNABBREV_TAC : term quotation -> tactic
Removes an abbreviation from a goal’s assumptions by substituting it out.
The argument to UNABBREV_TAC must be a quotation containing the name of a variable that is abbreviated in the current goal. In other words, when calling UNABBREV_TAC `v`, there must be an assumption of the form Abbrev(v = e) in the goal’s assumptions. This assumption is removed, and all occurrences of the variable v in the goal are replaced by e. If there are two abbreviation assumptions for v in the goal, the more recent is removed.
The goal
   Abbrev(v = 2 * x + 1), v + x < 10 ?- P(v)
is transformed by Q.UNABBREV_TAC `v` to
   2 * x + 1 + x < 10 ?- P(2 * x + 1)
Fails if there is no abbreviation of the required form in the goal’s assumptions, or if the quotation doesn’t parse to a variable.
HOL  Kananaskis-14