In Rudin's functional analysis text I do not understand the following step in theorem 6.4 (a).
$\phi -\phi _i \in (1- \delta _i ) W_i$
How do we get such delta? In particular how does $W_i$ being convex balanced set in $\mathcal D (\Omega)$ imply the existence of such $\delta$.
For reference I am attaching screenshot. Thanks in advance for the help.
