petrov's skewer opening


but if the opponent doesn't allow for the Grob gambit, then it's still called "Grob gambit with 2. Bg2," and no material has been sacrificed


not always, just look at this line


"a chess opening in which a player risks one or more pawns or a minor piece to gain an advantage in position" okay, I'll admit, I was wrong about the definition, but in the center gambit, you are sacrificing a pawn in order to gain an advantage

The double urusov I guess we could rename to "petrov's defense: urusov, mirror variation," but the copycat IS a gambit