An algebra homomorphism phi is a mapping that maps each element of an algebra A, called the source of phi, to an element of an algebra B, called the range of phi, such that for each pair x, y in A we have (xy)^phi = x^phi y^phi and (x + y)^phi = x^phi + y^phi.
An algebra homomorphism of unital algebras is unital if the zero-th power of elements in the source is mapped to the zero-th power of elements in the range.
At the moment, only operation homomorphisms are supported in GAP (see OperationHomomorphism for Algebras).
GAP 3.4.4