On binary relations without non-identical endomorphisms
arXiv:math/0003181 · doi:10.1007/s00010-002-8013-9
Abstract
On every set A there is a rigid binary relation, i.e. such a relation R that there is no homomorphism (A,R)->(A,R) except the identity (Vopenka et al. [1965]). We state two conjectures which strengthen this theorem. We prove these conjectures for some cardinalities.
3rd version, minor changes, PostScript, submitted to Aequationes Math