---
tag: JM98RN8HVF
kind: definition
name: Lambert quadrilateral
msc: [51F05, 51M09]
defines: MS263NBTRR
uses: [VKFPCSRNDH, 0GJAJC6TNZ]
sources:
  - url: https://en.wikipedia.org/wiki/Lambert_quadrilateral
---

## Definition

Let $ABCD$ be a convex quadrilateral in an [[absolute plane|VKFPCSRNDH]].
It is a *Lambert quadrilateral* if three of its [[angles|0GJAJC6TNZ]], say $\angle DAB$, $\angle ABC$ and $\angle BCD$, are right angles.

## Remarks

Example: in $\R^2$, the rectangle with vertices $(0,0)$, $(3,0)$, $(3,1)$, $(0,1)$ is a Lambert quadrilateral, since all four of its angles are right.
Non-example: the quadrilateral with vertices $(0,0)$, $(2,0)$, $(2,1)$, $(0,3)$ has right angles at $(0,0)$ and $(2,0)$ only, so it is not a Lambert quadrilateral.
The fourth angle $\angle CDA$ is right in the Euclidean plane and acute in the hyperbolic plane.