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decEquiv (Some a) (Some b) with (decEquiv a b)
decEquiv (Some a) (Some b) | (Yes prf) = Yes $ BothSame prf
decEquiv (Some a) (Some b) | (No ctra) = No $ fromNotEquiv ctra
decEquiv (Some a) (Some b) = case (decEquiv a b) of
(Yes prf) => Yes $ BothSame prf
(No ctra) => No $ fromNotEquiv ctra