let X, Y be ComplexNormSpace; :: thesis: for f being Point of (C_NormSpace_of_BoundedLinearOperators (X,Y)) holds 0 <= ||.f.||
let f be Point of (C_NormSpace_of_BoundedLinearOperators (X,Y)); :: thesis: 0 <= ||.f.||
reconsider g = f as Lipschitzian LinearOperator of X,Y by Def7;
consider r0 being object such that
A1: r0 in PreNorms g by XBOOLE_0:def 1;
reconsider r0 = r0 as Real by A1;
A2: ( not PreNorms g is empty & PreNorms g is bounded_above ) by Th26;
A3: (BoundedLinearOperatorsNorm (X,Y)) . f = upper_bound (PreNorms g) by Th29;

now :: thesis: for r being Real st r in PreNorms g holds
0 <= r

let r be Real; :: thesis: ( r in PreNorms g implies 0 <= r )
assume r in PreNorms g ; :: thesis: 0 <= r
then ex t being VECTOR of X st
( r = ||.(g . t).|| & ||.t.|| <= 1 ) ;
hence 0 <= r by CLVECT_1:105; :: thesis: verum

end;

then 0 <= r0 by A1;
then 0 <= upper_bound (PreNorms g) by A2, A1, SEQ_4:def 1;
hence 0 <= ||.f.|| by A3; :: thesis: verum