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Merge branch 'master' of ssh://schizomaniac.net//home/adamc/git-root/frap
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@ -189,6 +189,13 @@ Proof.
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equality.
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Qed.
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(* IMPORTANT NOTE: the proof above would *not* have worked with the orders of
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* variables [ls] and [acc] swapped in the lemma statement! Try the proof that
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* way to see what goes wrong. The problem is that the induction hypothesis
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* would be too weak. A single [acc] value would be fixed for the whole proof,
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* while we need [acc] to *vary* throughout the induction, by retaining a
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* universal quantifier for it in the IH. *)
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(* Concatenating the empty list has no effect. *)
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Lemma app_nil : forall A (ls : list A),
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ls ++ [] = ls.
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