  Let $G$ be a simple finite graph. A famous theorem of Dirac says that $G$ is
chordal if and only if $G$ admits a perfect elimination order. It is known by
Fr\"oberg that the edge ideal $I(G)$ of $G$ has a linear resolution if and only
if the complementary graph $G^c$ of $G$ is chordal. In this article, we discuss
some algebraic consequences of Dirac's theorem in the theory of homological
shift ideals of edge ideals. Recall that if $I$ is a monomial ideal,
$\mbox{HS}_k(I)$ is the monomial ideal generated by the $k$th multigraded
shifts of $I$. We prove that $\mbox{HS}_1(I)$ has linear quotients, for any
monomial ideal $I$ with linear quotients generated in a single degree. For and
edge ideal $I(G)$ with linear quotients, it is not true that
$\mbox{HS}_k(I(G))$ has linear quotients for all $k\ge0$. On the other hand, if
$G^c$ is a proper interval graph or a forest, we prove that this is the case.
Finally, we discuss a conjecture of Bandari, Bayati and Herzog that predicts
that if $I$ is polymatroidal, $\mbox{HS}_k(I)$ is polymatroidal too, for all
$k\ge0$. We are able to prove that this conjecture holds for all polymatroidal
ideals generated in degree two.
