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extra calc style #566

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extra calc style #566

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21 changes: 19 additions & 2 deletions templates/contribute/style.md
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Original file line number Diff line number Diff line change
Expand Up @@ -363,8 +363,25 @@ theorem reverse_reverse : ∀ (l : List α), reverse (reverse l) = l
_ = a :: l := rfl
```

However, because the expressions and proofs are relatively short, the following style
might be preferable in this situation.
The following style has the substantial advantage of having all lines be interchangeable, which is
particularly useful when editing the proof in eg VSCode:

```lean
import Init.Data.List.Basic

open List

theorem reverse_reverse : ∀ (l : List α), reverse (reverse l) = l
| [] => rfl
| (a :: l) => calc
reverse (reverse (a :: l))
_ = reverse (reverse l ++ [a]) := by rw [reverse_cons]
_ = reverse [a] ++ reverse (reverse l) := reverse_append _ _
_ = reverse [a] ++ l := by rw [reverse_reverse l]
_ = a :: l := rfl
```

If the expressions and proofs are relatively short, the following style is also an option:

```lean
import Init.Data.List.Basic
Expand Down