leanprover / leanprover/fp-lean
[Typo] Sect 9 exercise error: "'List.append_assoc' has already been declared"
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Description
January 2024 FPIL sect 9--not exactly a typo, but "technical error" seems too grand.
Prove that appending lists is associative using induction on lists:
theorem List.append_assoc (xs ys zs : List α) : xs ++ (ys ++ zs) = (xs ++ ys) ++ zs
List.append_assoc is defined in Basic.lean, so theorem List.append_assoc generates
error:
'List.append_assoc' has already been declared
Perhaps it's better to use a different name in the exercise. Easy enough to rename it though.
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Research direction
Start with the January 2024 FPIL section 9 exercise and inspect Basic.lean to confirm that List.append_assoc is already defined. Rename the theorem in the exercise so it no longer conflicts, then verify that the exercise no longer produces the duplicate-declaration error.
Written by the indexing model from the issue text.
Assessment
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- documentation
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- 45/100