Connectednesses of graphs and congruences

A connectedness of graphs is the analogue of the radical class of algebraic structures. The similarities (and differences) between these two theories and other radical theories have been explored at many different levels of generality. The recent development of a theory of congruences for graphs has opened up the possibility to explore and further strengthen this analogy. It is shown that a graph connectedness can be characterized with the use of congruences in an exact analogous way as the radical classes of associative rings using ideals.