Vlookup with multiple criteria

Scenario: IF(vlookup(a2,sheet1!X:X,1,false)=a2    AND(vlookup(b2,sheet1!Y:Y,false)=b2 THEN(vlookup(b2,sheet1!X:Z,3,false) IF NOT, blank   In other words, look up A & B on sheet1, look at sheet ...