reserve MS for satisfying_equiv MusicStruct;
reserve a,b,c,d,e,f for Element of MS;

theorem Th44:
  RAT_Music is satisfying_octave_constructible
  proof
  let frequency be Element of RAT_Music;
  consider fr,qr be positive Rational such that
A1: fr = frequency and
  qr = 2 * fr and
A2: [fr,qr] in octave(RAT_Music) by Th43;
  fr is Element of RAT_Music & qr is Element of RAT_Music by Th2;
  hence thesis by A1,A2;
end;
