Published online by Cambridge University Press: 09 August 2018
Given a Banach operator ideal $\mathcal A$, we investigate the approximation property related to the ideal of
$\mathcal A$-compact operators,
$\mathcal K_{\mathcal A}$-AP. We prove that a Banach space X has the
$\mathcal K_{\mathcal A}$-AP if and only if there exists a λ ≥ 1 such that for every Banach space Y and every R ∈
$\mathcal K_{\mathcal A}$(Y, X),
$$
\begin{equation}
R \in \overline {\{SR : S \in \mathcal F(X, X), \|SR\|_{\mathcal K_{\mathcal A}} \leq \lambda \|R\|_{\mathcal K_{\mathcal A}}\}}^{\tau_{c}}.
\end{equation}
$$
$\mathcal A$, we prove that a Banach space X has the
$\mathcal K_{(\mathcal A^{{\rm adj}})^{{\rm dual}}}$-AP if the dual space of X has the
$\mathcal K_{\mathcal A}$-AP.