A note on homologically smooth connected cochain DG algebras

In this paper, we obtain two interesting results on homologically smooth connected cochain DG algebras. More precisely, we show that any Koszul DG module in $\mathrm{D_{fg}}(A)$ is compact, when $A$ is a homologically smooth connected cochain DG algebra with a Noetherian cohomology graded algebra $H(A)$. And we prove that the homologically smoothness of $A$ is equivalent to $$\mathrm{D_{fg}}(A)=\mathrm{D}^c(A),$$ if $A$ is a Koszul connected cochain DG algebra such that $H(A)$ is a Noetherian graded algebra with a balanced dualizing complex.