Another proof for the removable singularities of the heat equation

We give two different simple proofs for the removable singularities of the heat equation in $(\Omega\setminus\{x_0\})\times (0,T)$ with $n\ge 3$. We also give a necessary and sufficient condition for removable singularities of the heat equation in $(\Omega\setminus\{x_0\})\times (0,T)$ for the case $n=2$.