theorem Th8:
  M1 is line_circulant & M2 is line_circulant & M3 is
  line_circulant implies M1+M2+M3 is line_circulant
proof
  assume that
A1: M1 is line_circulant & M2 is line_circulant and
A2: M3 is line_circulant;
  M1+M2 is line_circulant by A1,Th7;
  hence thesis by A2,Th7;
end;
