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feat(library/data/nat/wf): define measure using inverse image

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Leonardo de Moura 2014-11-11 00:28:46 -08:00
parent 4623a62ec3
commit 76711d00c1
1 changed files with 6 additions and 0 deletions
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library/data/nat/wf.lean
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@ -43,4 +43,10 @@ well_founded.intro
(assume Hlt : m < n, acc.inv iH Hlt)
(assume Heq : m = n, Heq⁻¹ ▸ iH))))
definition measure {A : Type} (f : A → nat) : A → A → Prop :=
inv_image lt f
definition measure.wf {A : Type} (f : A → nat) : well_founded (measure f) :=
inv_image.wf f lt.wf
end nat