theorem
  |.f1/f2.| = |.f1.|/|.f2.|
proof
  thus |.f1/f2.| = |.f1(#)(f2^).| by Th38
    .= |.f1.|(#)|.(f2^).| by Th29
    .= |.f1.|(#)((|.f2.|)^) by Th37
    .= |.f1.|/|.f2.| by RFUNCT_1:31;
end;
