Minimal Almost Convexity

In this article we show that the Baumslag-Solitar group $BS(1,2)$ is minimally almost convex, or $MAC$. We also show that $BS(1,2)$ does not satisfy Po'enaru’s almost convexity condition $P(2)$, and hence the condition $P(2)$ is strictly stronger than $MAC$. Finally, we show that the groups $BS(1,q)$ for $q\ge 7$ and Stallings’ non-$F{P}_3$ group do not satisfy $MAC$. As a consequence, the condition $MAC$ is not a commensurability invariant.