b5122b6a7b
This change * moves `termination_by` and `decreasing_by` next to the function they apply to * simplify the syntax of `termination_by` * apply the `decreasing_by` goal to all goals at once, for better interactive use. See the section in `RELEASES.md` for more details and migration advise. This is a hard breaking change, requiring developers to touch every `termination_by` in their code base. We decided to still do it as a hard-breaking change, because supporting both old and new syntax at the same time would be non-trivial, and not save that much. Moreover, this requires changes to some metaprograms that developers might have written, and supporting both syntaxes at the same time would make _their_ migration harder.
73 lines
1.9 KiB
Text
73 lines
1.9 KiB
Text
namespace Mutual
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mutual
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inductive Tree (α : Type u) where
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| node : TreeList α → Tree α
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| leaf : α → Tree α
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inductive TreeList (α : Type u) where
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| nil : TreeList α
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| cons : Tree α → TreeList α → TreeList α
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end
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mutual
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def Tree.size : Tree α → Nat
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| Tree.node l =>
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-- see "TODO: linarith" in Init.WFTactics
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have : sizeOf l < 1 + sizeOf l := by
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rw [Nat.add_comm]
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apply Nat.lt_succ_self
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sizeList l
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| Tree.leaf _ => 1
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-- use automatically synthesized size function, which is not quite the number of leaves
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termination_by t => sizeOf t
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def Tree.sizeList : TreeList α → Nat
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| TreeList.nil => 0
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| TreeList.cons t l =>
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have : sizeOf t < 1 + sizeOf t + sizeOf l := by
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rw [Nat.add_comm 1, Nat.add_assoc, Nat.add_comm 1, ← Nat.add_assoc]
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apply Nat.lt_succ_of_le
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apply Nat.le_add_right
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have : sizeOf l < 1 + sizeOf t + sizeOf l := by
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rw [Nat.add_comm 1, Nat.add_assoc, Nat.add_comm 1, ← Nat.add_assoc]
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apply Nat.lt_succ_of_le
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apply Nat.le_add_left
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t.size + sizeList l
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termination_by l => sizeOf l
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end
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end Mutual
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namespace Nested
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inductive Tree (α : Type u) where
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| node : List (Tree α) → Tree α
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| leaf : α → Tree α
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mutual
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def Tree.size : Tree α → Nat
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| Tree.node l =>
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have : sizeOf l < 1 + sizeOf l := by
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rw [Nat.add_comm]
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apply Nat.lt_succ_self
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sizeList l
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| Tree.leaf _ => 1
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termination_by t => sizeOf t
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def Tree.sizeList : List (Tree α) → Nat
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| [] => 0
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| t :: l =>
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have : sizeOf t < 1 + sizeOf t + sizeOf l := by
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rw [Nat.add_comm 1, Nat.add_assoc, Nat.add_comm 1, ← Nat.add_assoc]
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apply Nat.lt_succ_of_le
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apply Nat.le_add_right
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have : sizeOf l < 1 + sizeOf t + sizeOf l := by
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rw [Nat.add_comm 1, Nat.add_assoc, Nat.add_comm 1, ← Nat.add_assoc]
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apply Nat.lt_succ_of_le
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apply Nat.le_add_left
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t.size + sizeList l
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termination_by l => sizeOf l
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end
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end Nested
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