L

E

F

$l_1$

$E_1=\left\{x_1,x_3,x_4\right\}$

$F_1=\left\{x_2,x_5,x_6\right\}$

$l_{\text{2}}$

$E_{\text{2}}=\left\{x_{\text{2}},x_{\text{6}}\right\}$

$F_{\text{2}}=\left\{x_1,x_3,x_4,x_5\right\}$

$l_3$

$E_{\text{3}}=\left\{x_3,x_4,x_5\right\}$

$F_{\text{3}}=\left\{x_1,x_2,x_6\right\}$