Formal logarithm
= Formal logarithm
{title2=$\log_F$}
{wiki=Formal_group_law#Lie_algebra_of_a_formal_group_law}
Over a characteristic-zero field, a one-dimensional commutative formal group law has a unique strict isomorphism to the additive formal group, called its formal logarithm. It satisfies $\log_F(F(X,Y))=\log_F(X)+\log_F(Y)$.