Maybe the user mistakenly thought that they can actually ping you in that room, I am not really sure.
In any case, if their intention was to achieve that you are informed about the post on hsm, it seems that they achieved that - although in this unusual way.
Well, I suppose that anybody who has been around some Stack Exchange sites long enough has seen a fair share of @username being used in situations where the user is not really pingable.
The fact that Kostka numbers equals to Littlewood-Richardson coefficients for some partitions is already known $\colon$
\begin{align}
K_{\lambda \mu} = c_{\sigma \lambda}^\tau
\end{align}
where $\tau_i = (\mu_{i}, \mu_{i+1},\dots), \sigma_i = (\mu_{i+1}, \mu_{i+2},\dots)$.
For example, it is ...
The fact that Kostka numbers equals to Littlewood-Richardson coefficients for some partitions is already known $\colon$
\begin{align}
K_{\lambda \mu} = c_{\sigma \lambda}^\tau
\end{align}
where $\tau_i = (\mu_{i}, \mu_{i+1},\dots), \sigma_i = (\mu_{i+1}, \mu_{i+2},\dots)$.
For example, it is ...
