set MS = RAT_Music ;
let frequency be Element of RAT_Music; :: according to MUSIC_S1:def 42 :: thesis: ex q being Element of RAT_Music st [frequency,q] in fifth RAT_Music
consider fr, qr being positive Rational such that
A1: fr = frequency and
qr = (3 / 2) * fr and
A2: [fr,qr] in fifth RAT_Music by Th36;
( fr is Element of RAT_Music & qr is Element of RAT_Music ) by Th2;
hence ex q being Element of RAT_Music st [frequency,q] in fifth RAT_Music by A1, A2; :: thesis: verum