The motivic Lie algebra is contained in the Grothendieck-Teichmuller Lie algebra, and is isomorphic to the free graded Lie algebra with one generator in every odd degree >1. Using motivic MZV's one can define canonical generators for this algebra, but their arithmetic properties are very mysterious.
In this talk, I will explain how elements of the motivic Lie algebra admit a kind of Taylor expansion with a rich internal structure. This is closely connected with the theory of modular forms, universal elliptic motives, and some other unexpected algebraic objects.
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