some stuff about exact couples
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@ -131,12 +131,20 @@ definition SES_of_exact_couple_at_i : SES (ab_kernel i) A (ab_image i) :=
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fapply ab_group_first_iso_thm i,
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fapply ab_group_first_iso_thm i,
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end
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end
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definition kj_zero (a : A) : k (j a) = 1 :=
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begin
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exact sorry
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end
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definition j_factor : A →g (ab_kernel d) :=
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definition j_factor : A →g (ab_kernel d) :=
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begin
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begin
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fapply ab_hom_lift j,
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fapply ab_hom_lift j,
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intro a,
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intro a,
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unfold kernel_subgroup,
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unfold kernel_subgroup,
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exact sorry --refine ap (group_fun j) _,
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exact calc
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d (j a) = j (k (j a)) : rfl
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... = j 1 : by exact ap j (kj_zero a)
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... = 1 : to_respect_one,
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end
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end
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