~(L) ~(\forall \varepsilon > 0) (\exists \delta_L > 0) ~ t.d. ~ |x-c|<\delta_L \Rightarrow \left|\frac{F(x)-F(c)}{x-c} - L\right| < \varepsilon \\
~(D) ~(\forall \varepsilon > 0) (\exists \delta_D > 0) ~ t.d. ~ |v-c|<\delta_D \Rightarrow |f(v)-L| < \varepsilon \Rightarrow \\
~def. ~ \delta:=\min\{\delta_L, \delta_D\} \\
(\forall \varepsilon > 0) (\exists \delta > 0) ~ t.d. ~ |x-c|<\delta \Rightarrow \left|\frac{F(x)-F(c)}{x-c} - L \right| < \varepsilon ~ i ~ |f(x)-L| < \varepsilon \Rightarrow\\
\lim_{x \rightarrow c} \frac{F(x)-F(c)}{x-c} = L = \lim_{x \rightarrow c} f(x) = ~ :) ~ f(c)