文摘
This paper is devoted to the computation of the space \(\mathrm{H}_\mathrm{b}^2(\Gamma ,H;{\mathbb {R}})\) , where \(\Gamma \) is a free group of finite rank \(n\ge 2\) and \(H\) is a subgroup of finite rank. More precisely we prove that \(H\) has infinite index in \(\Gamma \) if and only if \(\mathrm{H}_\mathrm{b}^2(\Gamma ,H;{\mathbb {R}})\) is not trivial, and furthermore, if and only if there is an isometric embedding \(\oplus _\infty ^n\mathcal {D}({\mathbb {Z}})\hookrightarrow \mathrm{H}_\mathrm{b}^2(\Gamma ,H;{\mathbb {R}})\) , where \(\mathcal {D}({\mathbb {Z}})\) is the space of bounded alternating functions on \({\mathbb {Z}}\) equipped with the defect norm.