4. Try $\left( {\exists \varepsilon > 0} \right)\left( {\forall \delta > 0} \right)\left( {\exists x_0 } \right)\left[ {0 < \left| {x - x_0 } \right| < \delta \wedge \left| {f\left( {x_0 } \right) - L} \right| \geqslant \varepsilon } \right]$