272dd5533f
We are considering removing `.` as an alternative for `·` in the lambda dot notation (e.g., `(·+·)`). Reasons: - `.` is not a perfect replacement for `·` (e.g., `(·.insert ·)`) - `.` is too overloaded: `(f.x)` and `(f .x)` and `(f . x)`. We want to keep the first two.
14 lines
588 B
Text
14 lines
588 B
Text
def List.bubblesort [LT α] [DecidableRel (· < · : α → α → Prop)] (l : List α) : {l' : List α // l.length = l'.length} :=
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match l with
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| [] => ⟨[], rfl⟩
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| x :: xs =>
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match bubblesort xs with
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| ⟨[], h⟩ => ⟨[x], by simp[h]⟩
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| ⟨y :: ys, h⟩ =>
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if y < x then
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have : Nat.succ (length ys) < Nat.succ (length xs) := by rw [h, List.length_cons]; apply Nat.lt_succ_self
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let ⟨zs, he⟩ := bubblesort (x :: ys)
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⟨y :: zs, by simp[h, ← he]⟩
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else
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⟨x :: y :: ys, by simp[h]⟩
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termination_by _ => l.length
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