  Let $\mathscr{A}$ be an extension closed proper abelian subcategory of a
triangulated category $\mathscr{T}$, with no negative 1 and 2 extensions. From
this, two functors from $\Sigma\mathscr{A}\ast\mathscr{A}$ to $\mathscr{A}$ can
be constructed giving a snake lemma mirroring that of homology without needing
a t-structure. We generalize the concept of intermediate categories, which
originates from a paper by Enomoto and Saito, to the setting of proper abelian
subcategories and show that under certain assumptions this collection is in
bijection with torsion-free classes in $\mathscr{A}$.
