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

theorem Th37:
  RAT_Music is satisfying_fifth_constructible
  proof
    set MS = RAT_Music;
    let frequency be Element of MS;
    consider fr,qr be positive Rational such that
A1: fr = frequency and
    qr = (3 qua Rational) / 2 * fr and
A2: [fr,qr] in fifth(MS) by Th36;
    fr is Element of MS & qr is Element of MS by Th2;
    hence thesis by A1,A2;
  end;
