theorem Th22:
  M1 is col_circulant & M2 is col_circulant & M3 is col_circulant
  implies M1+M2+M3 is col_circulant
proof
  assume that
A1: M1 is col_circulant & M2 is col_circulant and
A2: M3 is col_circulant;
  M1+M2 is col_circulant by A1,Th21;
  hence thesis by A2,Th21;
end;
