Is there a Banach space $X$, $S$ an unbounded operator defined on a dense subspace $D$ of $X$ and a bounded operator $T$ on $X$ such that
$S+T|_D$
is bounded? What if $T$ is assumed to be compact?
Is there a Banach space $X$, $S$ an unbounded operator defined on a dense subspace $D$ of $X$ and a bounded operator $T$ on $X$ such that
$S+T|_D$
is bounded? What if $T$ is assumed to be compact?
Hint: the difference of two bounded operators is bounded.