bonjour
D = [ ( 1 /3 - 1 /2 ) : ( 1/4 - 1 /5 ) ] x [ ( 1/3 + 1/2 ) : ( 1/4 + 1 /5 ) ]
=[ ( 2/6 - 3 /6) : ( 5/20 - 4 /20 )] x [ ( 2/6 + 3 /6 ) : ( 5/20 + 4 /20 )]
= ( - 1 /6 : 1 /20 ) x ( 5/6 : 9 /20 )
= ( - 1 /6 * 20 ) x ( 5 /6 * 20/9 )
= - 20 /6 x 100 / 54
= - 10 /3 x 50 / 27
= - 150 / 81 = - 50 / 27
