Sentence:  In the line of operatic <WSD>trades</WSD> to cushion the budget , the Dallas Civic Opera will use San Francisco 's new Leni Bauer-Ecsy production of `` Lucia di Lammermoor '' this season , returning the favor next season when San Francisco uses the Dallas `` Don Giovanni '' , designed by Franco Zeffirelli . 
Meaning of the word marked with <WSD> tags:  a particular instance of buying or selling