Solution
= Solution
For an isomorphism $T$, if $\|T^{-1}(S-T)\|<1$, then
$$
S=T[I+T^{-1}(S-T)]
$$
is invertible by <neumann-series perturbation>.
= Solution
For an isomorphism $T$, if $\|T^{-1}(S-T)\|<1$, then
$$
S=T[I+T^{-1}(S-T)]
$$
is invertible by <neumann-series perturbation>.