Normality and the operation on cosets (defunct)

Let $G$ be a group, $H \leq G$ a subgroup that is not normal. Prove there exist cosets $H a$ and $H b$ such that $H a H b \neq H a b$ .

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Let $G$ be a group, $H\leq G$ a subgroup that is not normal. Prove there exist cosets $Ha$ and $Hb$ such that $HaHb\neq Hab$.