diff --git a/src/synthetic-homotopy-theory/flattening-lemma-sequential-colimits.lagda.md b/src/synthetic-homotopy-theory/flattening-lemma-sequential-colimits.lagda.md index 72ebcff9d9..0ad8516ee5 100644 --- a/src/synthetic-homotopy-theory/flattening-lemma-sequential-colimits.lagda.md +++ b/src/synthetic-homotopy-theory/flattening-lemma-sequential-colimits.lagda.md @@ -52,6 +52,9 @@ obtain a cocone which is again a sequential colimit. +The result may be read as +`colimₙ (Σ (a : Aₙ) P(iₙ a)) ≃ Σ (a : colimₙ Aₙ) P(a)`. + ## Definitions ### The sequential diagram for the flattening lemma @@ -116,21 +119,21 @@ so it suffices to invoke the flattening lemma for coequalizers. **Proof:** The diagram we construct is ```text - ---------> - Σ ((n, a) : Σ ℕ A) P(iₙ a) ---------> Σ ((n, a) : Σ ℕ A) P(iₙ a) -----> Σ (x : X) P(x) - | | | - assoc-Σ | ≃ assoc-Σ | ≃ id | ≃ - | | | - V ----------> V V - Σ (n : ℕ, a : Aₙ) P(iₙ a) ----------> Σ (n : ℕ, a : Aₙ) P(iₙ a) ------> Σ (x : X) P(x) , + -------> + Σ (n : ℕ) Σ (a : Aₙ) P(iₙ a) -------> Σ (n : ℕ) Σ (a : Aₙ) P(iₙ a) ----> Σ (x : X) P(x) + | | | + inv-assoc-Σ | ≃ inv-assoc-Σ | ≃ id | ≃ + | | | + V ---------> V V + Σ ((n, a) : Σ ℕ A) P(iₙ a) ---------> Σ ((n, a) : Σ ℕ A) P(iₙ a) -----> Σ (x : X) P(x) , ``` -where the top is the cofork obtained by coforkification of the cocone for the -flattening lemma, and the bottom is the cofork obtained by flattening the -coforkification of the original cocone. +where the top is the cofork corresponding to the cocone for the flattening +lemma, and the bottom is the cofork obtained by flattening the cofork +corresponding to the given base cocone. By assumption, the original cocone is a sequential colimit, which implies that -its coforkification is a coequalizer. The flattening lemma for coequalizers +its corresponding cofork is a coequalizer. The flattening lemma for coequalizers implies that the bottom cofork is a coequalizer, which in turn implies that the top cofork is a coequalizer, hence the flattening of the original cocone is a sequential colimit.