$\forall$$T$:Type, $l$:($T$ List), $x$, $y$, $z$:$T$.
\\[0ex]no\_repeats($T$;$l$) $\Rightarrow$ $x$ before $y$ $\in$ $l$ $\Rightarrow$ $y$ before $z$ $\in$ $l$ $\Rightarrow$ $x$ before $z$ $\in$ $l$