The GLB & LUB of Two Elements: Non-Unique Possibilities?

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Discussion Overview

The discussion centers on the uniqueness of the greatest lower bound (glb) and least upper bound (lub) of two elements in a lattice, exploring whether multiple equivalent or non-comparable glb or lub can exist.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions the uniqueness of glb and lub in a lattice, suggesting that it is possible for two equivalent or non-comparable glb or lub to exist.
  • Another participant asserts that glb and lub are unique in a lattice, referencing a definition from Wikipedia that states a lattice is a poset where any two elements have a unique glb and lub.
  • A subsequent reply acknowledges the previous point without further elaboration.
  • Another participant adds that in a poset, the glb and lub must be unique due to the property of antisymmetry.

Areas of Agreement / Disagreement

Participants express disagreement regarding the uniqueness of glb and lub, with some asserting uniqueness based on definitions and properties of lattices and posets, while others question this assertion.

Contextual Notes

The discussion does not resolve the question of uniqueness, and the definitions referenced may depend on specific interpretations or contexts within lattice theory.

Gear300
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The greatest lower bound and least upper bound of two elements a, b in a lattice do not have to be unique, do they? It could be the case that two equivalent or non-comparable glb or lub exist, right?
 
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They are unique in a lattice. By definition (according to wikipedia) a lattice a po-set where any two elements have a unique glb and lub (or infimum and supremum respectively).

http://en.wikipedia.org/wiki/Lattice_(order )
 
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Thanks.
 
In a poset the glb and lub must be unique by antisymmetry.
 

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