  Given formal differential operators $F_i$ on polynomial algebra in several
variables $x_1,...,x_n$, we discuss finding expressions $K_l$ determined by the
equation $\exp(\sum_i x_i F_i)(\exp(\sum_j q_j x_j)) = \exp(\sum_l K_l x_l)$
and their applications. The expressions for $K_l$ are related to the coproducts
for deformed momenta for the noncommutative space-times of Lie algebra type and
also appear in the computations with a class of star products. We find
combinatorial recursions and derive formal differential equations for finding
$K_l$. We elaborate an example for a Lie algebra $su(2)$, related to a quantum
gravity application from the literature.
