Hello. The image corresponds to the book of functional analysis volume II by barry simon. I know that any function $f$ in $L^p$ can be identified with a tempered distribution $T_f$ defined by $T_f \varphi=\int f\varphi,\quad \varphi$ test function but what does it mean that $\Delta \varphi \in L^2$ in the sense of distributions? does it mean that $T_{\Delta u}\in L^2$ (in the classical sense)? thank you.