Baseball’s greatest rivalry is now one for the books.

The New York Public Library and Boston Public Library have teamed up to have some fun around the American League Division Series between longtime, bitter rivals The New York Yankees and Boston Red Sox.

The two public libraries made a bookish bet:

• If the Yankees win, Boston Public Library will create a recommended list of books about New York and promote it prominently. President David Leonard also needs to wear a Yankees cap, and The New York Public Library will receive Boston Cream Pies.

• If the Red Sox win, The New York Public Library will create a recommended list of books about Boston and promote it prominently. President Tony Marx also needs to wear a Red Sox cap, and The Boston Public Library will receive New York bagels.

In addition to the wager, watch for the two systems to keep the rivalry going on social media throughout the best-of-five series. Follow @nypl and @BPLBoston to cheer on your team.

Let the games begin! We're betting @bplboston that the @yankees will beat the @redsox in the #ALDS. The losing team’s library will recommend a book list about the winning team’s city! pic.twitter.com/ef8akDFf0u

— NY Public Library (@nypl) October 5, 2018

Well, well, well . . . looks like the @yankees and @redsox meet again. We’re ready for our own literary #ALDS with @bplboston!https://t.co/ADb88hPyJM pic.twitter.com/Ipy7FfphF8

— NY Public Library (@nypl) October 5, 2018

Hey @bplboston - legends don’t stress. Hope the @redsox are ready for a classic @yankees fight. #ALDS pic.twitter.com/92PHJlGRpE

— NY Public Library (@nypl) October 7, 2018

hey, @redsox—at least enjoy the bagels while you’re here. Bring a few back for @bplboston ⚾️ #ALDS https://t.co/pH8TvWrG4B pic.twitter.com/vTY5HennR3

— NY Public Library (@nypl) October 8, 2018

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Doesn’t matter if it’s 1928 or 2018, the @yankees are calm and cool —but hey, @redsox—at least enjoy the bagels while you’re here. Bring a few back for @bplboston ⚾️ ⠀ (Image via @nypl Digital Collections; ID 101050)

A post shared by The New York Public Library (@nypl) on Oct 8, 2018 at 3:55pm PDT

What’s that old saying—you win some, you lose some by 15 runs? No need to be alarmed, @yankees fans; keep your eyes on the big game. #ALDS pic.twitter.com/cNCrW4BM9m

— NY Public Library (@nypl) October 9, 2018