Word problems

The talk will be an introduction to the world of word problems, in particular word problems for varieties of semigroups. Attention will be paid especially to commutative semigroups (reversible Petri nets). I intend to prove Redei's Theorem on finitely generated commutative semigroups and, if time allows, the decidability of the (uniform) word problem for commutative semigroups and the undecidability of the uniform word problem for finite semigroups.