41 lines
1.1 KiB
Text
41 lines
1.1 KiB
Text
/-
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Copyright (c) 2015 Floris van Doorn. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Module: hit.suspension
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Authors: Floris van Doorn
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Declaration of suspension
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-/
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import .pushout
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open pushout unit eq
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definition suspension (A : Type) : Type := pushout (λ(a : A), star) (λ(a : A), star)
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namespace suspension
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definition north (A : Type) : suspension A :=
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inl _ _ star
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definition south (A : Type) : suspension A :=
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inr _ _ star
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definition merid {A : Type} (a : A) : north A = south A :=
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glue _ _ a
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protected definition rec {A : Type} {P : suspension A → Type} (PN : P !north) (PS : P !south)
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(Pmerid : Π(a : A), merid a ▹ PN = PS) (y : suspension A) : P y :=
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begin
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fapply (pushout.rec_on _ _ y),
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{ intro u, cases u, exact PN},
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{ intro u, cases u, exact PS},
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{ exact Pmerid},
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end
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protected definition rec_on {A : Type} {P : suspension A → Type} (y : suspension A)
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(PN : P !north) (PS : P !south) (Pmerid : Π(a : A), merid a ▹ PN = PS) : P y :=
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rec PN PS Pmerid y
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end suspension
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