EN
CONTENTS
1. Introduction........................................................................................................................5
2. Definition, basic examples and properties of multisemilattices...........................................6
3. The subdirectly irreducibles..............................................................................................13
4. The lattice of subvarieties of $D_n$.................................................................................18
5. Subvarieties of $D_n$ defined by identities involving at most two operation symbols......24
6. Some further comments and open problems....................................................................34
References...........................................................................................................................40