Extensive approach to absolute homogeneity

Abstract

The main aim of the paper is to study in greater detail absolutely homogeneous structures (that is, objects with the property that each partial isomorphism extends to a global automorphism), with special emphasis on metric spaces and (possibly infinite, full) graphs with edge-coloring. Besides, a general categorical approach to this concept is presented. The main achievement of the paper is the discovery of one-to-one correspondence between absolutely homogeneous objects and certain classes (that become sets when isomorphic objects are identified) of "finite" objects that satisfy a few quite general axioms (such as amalgamation and heredity). It is also introduced and discussed in detail the concept of products for graphs with edge-coloring (that produces an absolutely homogeneous graph provided all factors are so). Among the most significant results of the paper, it is worth mentioning a full classification (up to isometry) of all absolutely homogeneous ultrametric spaces as well as of all absolutely homogeneous graphs with edge-coloring in which all triangles are isosceles or in which all triangles are (precisely) tricolored.