  We show that morphisms from n A_infinity-algebras to a single one are maps
over an operad module with n+1 commuting actions of the operad A_infinity,
whose algebras are conventional A_infinity-algebras. Similar statement holds
for homotopy unital A_infinity-algebras. The operad A_infinity and modules over
it have two useful gradings related by isomorphisms which change the degree.
The composition of A_infinity-morphisms with several entries is presented as a
convolution of a coalgebra-like and an algebra-like structures. For this sake
notions of lax Cat-span multicategories and multifunctors are introduced. They
are lax versions of strict multicategories and multifunctors associated with
the monad of free strict monoidal category.
