let b, d, a, c be real number ; :: thesis: ( 0 < b & d < 0 & a * d <= c * b implies c / d <= a / b )
assume A1: ( b > 0 & d < 0 & a * d <= c * b ) ; :: thesis: c / d <= a / b
then (a * d) / b <= c by Th81;
then (a / b) * d <= c by XCMPLX_1:75;
hence c / d <= a / b by A1, Th80; :: thesis: verum