let p, q, r, s be ExtReal; :: thesis: ( r < s & ].r,s.[ c= ].p,q.[ implies ( p <= r & s <= q ) )
assume that
A1: r < s and
A2: ].r,s.[ c= ].p,q.[ ; :: thesis: ( p <= r & s <= q )
].p,q.[ c= [.p,q.] by Th25;
then ].r,s.[ c= [.p,q.] by A2;
hence ( p <= r & s <= q ) by A1, Th51; :: thesis: verum