Generalization of the ABC theorem on locally nilpotent derivations

We obtain a generalization of the ABC Theorem on locally nilpotent derivations to the case of the polynomials with $m$ monomials such that each variable is included just in a sole monomial. As applications of this result we provide some construction of rigid and semirigid algebras and describe the Makar-Limanov invariant of algebras of a special form.