Library.merge/OrdList.union: optimize the important special case where the tables coincide -- NOTE: this changes both the operational behaviour and the result for non-standard eq/ord notion;

reduced verbosity;

made SML/NJ happy

tuned interpunctation

strip_abss: always strip abstractions as far as possible, without keeping alternatives (which appear to be redundant anyway, but cause significant slowdown since discrimination nets collapse abstractions);

close/all_assm_tac: finish all subgoals from left to right (cf. Proof.goal_tac a28d83e903ce) -- NB: ALLGOALS/THEN_ALL_NEW operate from right to left;

reverted abbreviations: improved performance via Item_Net.T;

export match_rew -- useful for implementing "procs" for rewrite_term;