by placing a small sub-matrix $\hat{H}$ of size $h × w$ next
to each other and by shifting down by one row.
Thanks to this special form of $H$, one can represent
-every solution of $m=Hy$ as a path through a trellis.
+any solution of $m=Hy$ as a path through a trellis.
Next, the process of finding $y$ consists in two stages: a forward and a backward part.
\begin{enumerate}