$\forall$$T$:Type, $L$:($T$ List), $a$, $b$, $c$:$T$.
\\[0ex]no\_repeats($T$;$L$) $\Rightarrow$ adjacent($T$;$L$;$a$;$b$) $\Rightarrow$ adjacent($T$;$L$;$a$;$c$) $\Rightarrow$ ($b$ = $c$)