We show that the transition of Josephson junctions between the conventional
and pi states caused by the decrease in temperature induces in a regular
two-dimensional array of such junctions not just a single phase transition
between two phases with different ordering but a sequence of two, three or four
phase transitions. The corresponding phase diagrams are constructed for the
cases of bipartite (square or honeycomb) and triangular lattices.Comment: 5 pages, v2: as published in EP