Pasting lemma #
This file proves the pasting lemma for pullbacks. That is, given the following diagram:
X₁ - f₁ -> X₂ - f₂ -> X₃
| | |
i₁ i₂ i₃
∨ ∨ ∨
Y₁ - g₁ -> Y₂ - g₂ -> Y₃
if the right square is a pullback, then the left square is a pullback iff the big square is a pullback.
Main results #
bigSquareIsPullback
shows that the big square is a pullback if both the small squares are.leftSquareIsPullback
shows that the left square is a pullback if the other two are.pullbackRightPullbackFstIso
shows, using thepullback
API, thatW ×[X] (X ×[Z] Y) ≅ W ×[Z] Y
.
Given
X₁ - f₁ -> X₂ - f₂ -> X₃ | | | i₁ i₂ i₃ ∨ ∨ ∨ Y₁ - g₁ -> Y₂ - g₂ -> Y₃
Then the big square is a pullback if both the small squares are.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Given
X₁ - f₁ -> X₂ - f₂ -> X₃ | | | i₁ i₂ i₃ ∨ ∨ ∨ Y₁ - g₁ -> Y₂ - g₂ -> Y₃
Then the big square is a pushout if both the small squares are.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Given
X₁ - f₁ -> X₂ - f₂ -> X₃ | | | i₁ i₂ i₃ ∨ ∨ ∨ Y₁ - g₁ -> Y₂ - g₂ -> Y₃
Then the left square is a pullback if the right square and the big square are.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Given
X₁ - f₁ -> X₂ - f₂ -> X₃ | | | i₁ i₂ i₃ ∨ ∨ ∨ Y₁ - g₁ -> Y₂ - g₂ -> Y₃
Then the right square is a pushout if the left square and the big square are.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The canonical isomorphism W ×[X] (X ×[Z] Y) ≅ W ×[Z] Y
Equations
- One or more equations did not get rendered due to their size.
Instances For
The canonical isomorphism (Y ⨿[X] Z) ⨿[Z] W ≅ Y ×[X] W
Equations
- One or more equations did not get rendered due to their size.