theorem
  ((0.X,x) to_power (m+n))` = ((0.X,x)to_power m)`\(0.X,x)to_power n
proof
  ((0.X,x)to_power (m+n))` =(((0.X,x)to_power m)\((0.X,x)to_power n)`)` by Th13
    .=(((0.X,x)to_power m)`)\(((0.X,x)to_power n)`)` by BCIALG_1:9;
  hence thesis by Th12;
end;
