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 )
].r,s.[ c= [.r,s.[ by Th22;
then ].r,s.[ c= [.p,q.] by A2;
hence ( p <= r & s <= q ) by A1, Th51; :: thesis: verum