$\vdash$  $\forall$$T$:Type, $l_{1}$, $l_{2}$, $l_{3}$:($T$ List). fseg($T$;$l_{1}$;$l_{2}$) $\Rightarrow$ fseg($T$;$l_{2}$;$l_{3}$) $\Rightarrow$ fseg($T$;$l_{1}$;$l_{3}$)