  The mod 2 Steenrod algebra $\mathcal{A}_2$ can be defined as the quotient of
the mod 2 Leibniz--Hopf algebra $\mathcal{F}_2$ by the Adem relations. Dually,
the mod 2 dual Steenrod algebra $\mathcal{A}_2^*$ can be thought of as a
sub-Hopf algebra of the mod 2 dual Leibniz--Hopf algebra $\mathcal{F}_2^*$. We
study $\mathcal{A}_2^*$ and $\mathcal{F}_2^*$ from this viewpoint and give
generalisations of some classical results in the literature.
