Let $R$ be a ring, and let $n, d$ be non-negative integers. A right $R$-module $M$ is called $(n, d)$-projective if $Ext^{d+1}_R(M, A)=0$ for every $n$-copresented right $R$-module $A$. $R$ is called right $n$-cocoherent if every $n$-copresented right $R$-module is $(n+1)$-coprese-nted, it is called a right co-$(n,d)$-ring if every right $R$-module is $(n, d)$-projective. $R$...
