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单词 LatticeInterval
释义

lattice interval


Definition. Let L be a latticeMathworldPlanetmath. A subset I of L is called a lattice interval, or simply an if there exist elements a,bL such that

I={tLatb}:=[a,b].

The elements a,b are called the endpoints of I. Clearly a,bI. Also, the endpoints of a lattice interval are unique: if [a,b]=[c,d], then a=c and b=d.

Remarks.

  • It is easy to see that the name is derived from that of an interval on a number line. From this analogyMathworldPlanetmath, one can easily define lattice intervals without one or both endpoints. Whereas an interval on a number line is linearly orderedPlanetmathPlanetmath, a lattice interval in general is not. Nevertheless, a lattice interval I of a lattice L is a sublattice of L.

  • A bounded latticeMathworldPlanetmath is itself a lattice interval: [0,1].

  • A prime interval is a lattice interval that contains its endpoints and nothing else. In other words, if [a,b] is prime, then any c[a,b] implies that either c=a or c=b. Simply put, b covers a. If a lattice L contains 0, then for any aL, [0,a] is a prime interval iff a is an atom.

  • Since no operationsMathworldPlanetmath of meet and join are used, all of the above discussion can be generalized to define an interval in a poset.

  • Given a lattice L, let be the collectionMathworldPlanetmath of all lattice intervals without endpoints, we can form a topolgy on L with as the subbasis. This does not insure that and are continuousMathworldPlanetmathPlanetmath, so that L with this topological structure may not be a topological lattice.

  • Locally Finite Lattice. A lattice that is derived based on the concept of lattice interval is that of a locally finite lattice. A lattice L is locally finitePlanetmathPlanetmathPlanetmath iff every one of its interval is finite. Unless the lattice is finite, a locally finite lattice, if infiniteMathworldPlanetmath, is either topless or bottomless.

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更新时间:2025/5/4 1:00:50