Б30
БАШ НА БАШ
highly collInvarfixed WO 1. \Б-30 менять(ся), обменивать и т. п.
adv (in refer, to goods) (to exchange) one thing for another without additional payment, without adding anything: (make) an even swap (trade).
2. ( subj-compl with бытье ( subj: usu. всё), adv, or indep. sent) an action (is undertaken), form of behavior (is demonstrated) etc in retaliation or reciprocation for a similar action, form of behavior etc
tit for tat.