4 N ov 2 01 7 REVERSIBILITY OF DISCONNECTED STRUCTURES

A relational structure is called reversible iff every bijective endomorphism of that structure is an automorphism. We give several equivalents of that property in the class of disconnected binary structures and some its subclasses. For example, roughly speaking and denoting the set of integers by Z, a structure having reversible components is reversible iff its components can not be “merged” by condensations (bijective homomorphisms) and each Zsequence of condensations between different components must be, in fact, a sequence of isomorphisms. We also give equivalents of reversibility in some special classes of structures. For example, we characterize CSB linear orders of a limit type and show that a disjoint union of such linear orders is a reversible poset iff the corresponding sequence of order types is finite-to-one. 2010Mathematics Subject Classification: 03C07, 03E05, 05C40, 06A06.