Let f and g be two non-zero derivable functions and g' = f ³ and f ' = – g³.  If $\mathcal{l}$ is the value of $\underset{\mathrm{x}\to 2}{\mathrm{Lim}}\sqrt{\mathrm{sgn}\left(\frac{\left\{\mathrm{x}\right\}}{\left[\mathrm{x}\right]}\right)}$ and m = $\frac{{\mathrm{f}}^4\left(2\right)+{\mathrm{g}}^4\left(2\right)}{{\mathrm{f}}^4\left(0\right)+{\mathrm{g}}^4\left(0\right)}$ then find the value of ($\mathcal{l}$ + m).