Inverse monoids and rational subsets of related groups.
Let be a one-dimensional analytically irreducible ring and let be an integral ideal of . We study the relation between the irreducibility of the ideal in and the irreducibility of the corresponding semigroup ideal . It turns out that if is irreducible, then is irreducible, but the converse does not hold in general. We collect some known results taken from [5], [4], [3] to obtain this result, which is new. We finally give an algorithm to compute the components of an irredundant decomposition...
According to S. Krstić, there are only four quadratic varieties which are closed under isotopy. We give a simple procedure generating quadratic identities and deciding which of the four varieties they define. There are about 37000 such identities with up to five variables.