Well-pointed coalgebras

Abstract

For endofunctors of varieties preserving intersections, a new description of the final coalgebra and the initial algebra is presented: the former consists of all well-pointed coalgebras. These are the pointed coalgebras having no proper subobject and no proper quotient. The initial algebra consists of all well-pointed coalgebras that are well-founded in the sense of Osius and Taylor. And initial algebras are precisely the final well-founded coalgebras. Finally, the initial iterative algebra consists of all finite wellpointed coalgebras. Numerous examples are discussed e.g. automata, graphs, and labeled transition systems. ©J. Adámek, S. Milius, L. S. Moss, and L. Sousa.