Let $\mathbb{E}$ be a (real or complex) Banach space and let $\mathbb{B}(\mathbb{E})$ be the Banach Space of continuous (bounded) linear operators from $\mathbb{E}$ into $\mathbb{E}$, with the operator norm.
An operator $P \in \mathbb{B}(\mathbb{E})$ is called projection if $P^2=P$.
Are there other characterisations of projection operators in Banach Spaces ?
Where can such characterisations be found ?