Team 1 begins by going to Team 2 and offers X for Y.
Team 2 counters by saying, I don't think X is as valuable as Y, so I want X and Z for Y. That would be a "two for one."
Team 1 says, I don't want to give you a whole "extra" player, but if you trade me Y for X, which works in my favor, I'll offer you A for B, which works in yours. Now it's "two for two."
So if team 2 agrees that the "package" X+A = the Y+B "package" (and both sides get what they want), the deal gets done.
Is that how a "multiplayer" dialog might go or are there other routes?
(An example was Sean Burnett and Nyger Morgan for Joel Hanrahan and Lastings Milledge between the Pittsburgh Pirates and Washington Nationals some years ago, from my own piece: (I'm not referring to a veterans for prospects trade, that's a separate...