
theorem Th23:
  for MS being satisfying_equiv MusicStruct
  for a,b,c,d,e,f being Element of MS holds
  a,b equiv c,d & c,d equiv e,f implies a,b equiv e,f
  proof
    let MS be satisfying_equiv MusicStruct;
    let a,b,c,d,e,f be Element of MS;
    assume a,b equiv c,d & c,d equiv e,f;
    then (the Ratio of MS).(a,b) = (the Ratio of MS).(c,d) &
    (the Ratio of MS).(c,d) = (the Ratio of MS).(e,f) by Def08a;
    hence thesis by Def08a;
  end;
