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Michael Zhang 2024-09-15 19:42:46 -05:00
parent 16c5e3ab81
commit 764351ccb1

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@ -118,26 +118,26 @@ We can write functions going back and forth:
Σ2→S¹ (merid false i) = loop i -- for the path going through false, let's map this to the loop Σ2→S¹ (merid false i) = loop i -- for the path going through false, let's map this to the loop
Σ2→S¹ (merid true i) = base -- for the path going through true, let's map this to refl Σ2→S¹ (merid true i) = base -- for the path going through true, let's map this to refl
S¹→Σ2 : S¹ → Susp Bool -- S¹→Σ2 : S¹ → Susp Bool
S¹→Σ2 base = north -- S¹→Σ2 base = north
S¹→Σ2 (loop i) = {! !} -- S¹→Σ2 (loop i) = {! !}
``` ```
Now, to finish showing the equivalence, we need to prove that these functions concatenate into the identity in both directions: Now, to finish showing the equivalence, we need to prove that these functions concatenate into the identity in both directions:
``` ```
rightInv : section Σ2→S¹ S¹→Σ2 -- rightInv : section Σ2→S¹ S¹→Σ2
rightInv = {! !} -- rightInv = {! !}
leftInv : retract Σ2→S¹ S¹→Σ2 -- leftInv : retract Σ2→S¹ S¹→Σ2
leftInv = {! !} -- leftInv = {! !}
``` ```
And this gives us our equivalence! And this gives us our equivalence!
``` ```
Σ2≃S¹ : Susp Bool ≃ S¹ -- Σ2≃S¹ : Susp Bool ≃ S¹
Σ2≃S¹ = isoToEquiv (iso Σ2→S¹ S¹→Σ2 rightInv leftInv) -- Σ2≃S¹ = isoToEquiv (iso Σ2→S¹ S¹→Σ2 rightInv leftInv)
``` ```
In fact, we can also show that the $2$-sphere is the suspension of the $1$-sphere. In fact, we can also show that the $2$-sphere is the suspension of the $1$-sphere.