Baker 1905 + Campbell 1898 + Hausdorff 1906: log(exp X exp Y) = X + Y + (1/2)[X,Y] + (1/12)([X,[X,Y]] - [Y,[X,Y]]) + ...; basis of Lie-group multiplication near identity.
Baker 1905 + Campbell 1898 + Hausdorff 1906: log(exp X exp Y) = X + Y + (1/2)[X,Y] + (1/12)([X,[X,Y]] - [Y,[X,Y]]) + ...; basis of Lie-group multiplication near identity.