Redei's theorem asserts that any finitely generated monoid is finitely presented. There are many proofs of this result in the literature. Some of them use only ``semigroupist'' techniques while others use also some Commutative Algebra machinery. In this talk we will focus our attention in the second approach. The second part of the seminar deals with some kind of monoids for which the concepts of minimal presentation with respect to inclusion and cardinality coincide. In order to get a characterization of these monoids we prove a version of Nakayama's Lemma for rings graded by a monoid.