Common Fixed Points of Increasing Operators in Posets and Related Semilattice Properties

An extension of a well known theorem of R. DeMarr [Common fixed points for isotone mappings, Colloquium Math., 13 (1964), 45-48] for commuting families of increasing operators in posets is studied and we establish two corollaries concerning semilattice properties of the set of their common fixed points. Mathematics Subject Classification: 47H10, 54H25