Deligne’s letters to Breen

These letters were sent by Pierre Deligne to Larry Breen in February, 1994.

For more information on the construction, and applications to Poisson geometry, see:

A Darboux theorem for Hamiltonian operators in the formal calculus of variations, Duke J. Math. 111 (2002), 535-560.

For an extension of this construction to higher order n-groupoids, see:

Lie theory for nilpotent L∞ algebras,
Ann. of Math. (2) 170 (2009), no. 1, 271–301.

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