theorem Th1:
  x0>0 & x1>0 implies
  log(number_e,x0) - log(number_e,x1) = log(number_e,x0/x1)
proof
  assume
A1:x0>0 & x1>0;
  number_e > 1 by TAYLOR_1:11,XXREAL_0:2;
  hence thesis by A1,POWER:54;
end;
