Published online by Cambridge University Press: 20 November 2018
Building on our previous work, we study the non-relative homology of quantum group convolution algebras. Our main result establishes the equivalence of amenability of a locally compact quantum group   $\mathbb{G}$  and 1-injectivity of
 $\mathbb{G}$  and 1-injectivity of   ${{L}^{\infty }}\left( \widehat{\mathbb{G}} \right)$  as an operator
 ${{L}^{\infty }}\left( \widehat{\mathbb{G}} \right)$  as an operator   ${{L}^{1}}\left( \widehat{\mathbb{G}} \right)$ -module. In particular, a locally compact group
 ${{L}^{1}}\left( \widehat{\mathbb{G}} \right)$ -module. In particular, a locally compact group   $G$  is amenable if and only if its group von Neumann algebra
 $G$  is amenable if and only if its group von Neumann algebra   $\text{VN}\left( G \right)$  is 1-injective as an operator module over the Fourier algebra
 $\text{VN}\left( G \right)$  is 1-injective as an operator module over the Fourier algebra   $A\left( G \right)$ . As an application, we provide a decomposability result for completely bounded
 $A\left( G \right)$ . As an application, we provide a decomposability result for completely bounded   ${{L}^{1}}\left( \widehat{\mathbb{G}} \right)$ -module maps on
 ${{L}^{1}}\left( \widehat{\mathbb{G}} \right)$ -module maps on   ${{L}^{\infty }}\left( \widehat{\mathbb{G}} \right)$ , and give a simplified proof that amenable discrete quantum groups have co-amenable compact duals, which avoids the use of modular theory and the Powers-Størmer inequality, suggesting that our homological techniques may yield a new approach to the open problem of duality between amenability and co-amenability.
 ${{L}^{\infty }}\left( \widehat{\mathbb{G}} \right)$ , and give a simplified proof that amenable discrete quantum groups have co-amenable compact duals, which avoids the use of modular theory and the Powers-Størmer inequality, suggesting that our homological techniques may yield a new approach to the open problem of duality between amenability and co-amenability.
 . 
               Ann. of Math. (2) 
               104(1976), no. 1, 73–115.http://dx.doi.Org/10.2307/1971057
            Google Scholar
. 
               Ann. of Math. (2) 
               104(1976), no. 1, 73–115.http://dx.doi.Org/10.2307/1971057
            Google Scholar . 
               Trans. Amer. Math. Soc. 
               360(2008), no. 3,1133–1161.http://dx.doi.org/10.1090/S0002-9947-07-03940-2
            Google Scholar
. 
               Trans. Amer. Math. Soc. 
               360(2008), no. 3,1133–1161.http://dx.doi.org/10.1090/S0002-9947-07-03940-2
            Google Scholar