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''Dedekind lattice''
 
''Dedekind lattice''
  
A [[Lattice|lattice]] in which the modular law is valid, i.e. if <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m0644601.png" />, then <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m0644602.png" /> for any <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m0644603.png" />. This requirement amounts to saying that the identity <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m0644604.png" /> is valid. Examples of modular lattices include the lattices of subspaces of a linear space, of normal subgroups (but not all subgroups) of a group, of ideals in a ring, etc. A lattice with a [[composition sequence]] is a modular lattice if and only if there exists on it a dimension function <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m0644605.png" />, i.e. an integer-valued function such that <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m0644606.png" /> and such that if the interval <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m0644607.png" /> is prime, it follows that <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m0644608.png" />. If <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m0644609.png" />, if none of the elements <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446010.png" /> can be represented as a product of elements other than itself and if
+
A [[Lattice|lattice]] in which the modular law is valid, i.e. if $  a \leq  c $,  
 +
then $  ( a + b ) c = a + bc $
 +
for any $  b $.  
 +
This requirement amounts to saying that the identity $  ( ac + b ) c = ac + bc $
 +
is valid. Examples of modular lattices include the lattices of subspaces of a linear space, of normal subgroups (but not all subgroups) of a group, of ideals in a ring, etc. A lattice with a [[composition sequence]] is a modular lattice if and only if there exists on it a dimension function $  d $,  
 +
i.e. an integer-valued function such that $  d ( x + y ) + d ( xy ) = d ( x ) + d ( y ) $
 +
and such that if the interval $  [ a , b] $
 +
is prime, it follows that $  d ( b ) = d ( a ) + 1 $.  
 +
If $  w = a _ {1}  ^ {(} 1) \dots a _ {m _ {1}  }  ^ {(} 1) = a _ {1}  ^ {(} 2) \dots a _ {m _ {2}  }  ^ {(} 2) $,  
 +
if none of the elements $  a _ {i}  ^ {(} k) $
 +
can be represented as a product of elements other than itself and if
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446011.png" /></td> </tr></table>
+
$$
 +
a _ {1}  ^ {(} k) \dots a _ {i-} 1  ^ {(} k) a _ {i+} 1  ^ {(} k) \dots a _ {mk}  ^ {(} k)  \Nle  a _ {i}  ^ {(} k) ,
 +
$$
  
then <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446012.png" /> and for any <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446013.png" /> it is possible to find an element <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446014.png" /> such that
+
then $  m _ {1} = m _ {2} $
 +
and for any $  a _ {i}  ^ {(} 1) $
 +
it is possible to find an element $  a _ {j}  ^ {(} 2) $
 +
such that
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446015.png" /></td> </tr></table>
+
$$
 +
= a _ {1}  ^ {(} 1) \dots a _ {i-} 1  ^ {(} 1) a _ {j}  ^ {(} 2)
 +
a _ {i+} 1  ^ {(} 1) \dots a _ {m _ {1}  }  ^ {(} 1) ,
 +
$$
  
[[#References|[3]]], [[#References|[6]]]. Non-zero elements <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446016.png" /> of a modular lattice with a zero 0 are said to be independent if <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446017.png" /> for all <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446018.png" />. This definition makes it possible to generalize many properties of systems of linearly independent vectors [[#References|[3]]], [[#References|[5]]], [[#References|[6]]]. If <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446019.png" /> are independent, their sum is denoted by <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446020.png" />. Ore's theorem: If a modular lattice has a composition sequence and if
+
[[#References|[3]]], [[#References|[6]]]. Non-zero elements $  a _ {1} \dots a _ {n} $
 +
of a modular lattice with a zero 0 are said to be independent if $  ( a _ {1} + \dots + a _ {i-} 1 + a _ {j+} 1 + \dots + a _ {n} ) a _ {i} = 0 $
 +
for all $  i $.  
 +
This definition makes it possible to generalize many properties of systems of linearly independent vectors [[#References|[3]]], [[#References|[5]]], [[#References|[6]]]. If $  a _ {1} \dots a _ {n} $
 +
are independent, their sum is denoted by $  a _ {1} \oplus \dots \oplus a _ {n} $.  
 +
Ore's theorem: If a modular lattice has a composition sequence and if
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446021.png" /></td> </tr></table>
+
$$
 +
= a _ {1}  ^ {(} 1) \oplus \dots \oplus a _ {m _ {1}  }  ^ {(} 1)  = \
 +
a _ {1}  ^ {(} 2) \oplus \dots \oplus a _ {m _ {2}  }  ^ {(} 2) ,
 +
$$
  
none of the elements <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446022.png" /> being representable as a sum of two independent elements, then <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446023.png" /> and for each <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446024.png" /> it is possible to find an element <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446025.png" /> such that
+
none of the elements $  a _ {i}  ^ {(} k) $
 +
being representable as a sum of two independent elements, then $  m _ {1} = m _ {2} $
 +
and for each $  a _ {i}  ^ {(} 1) $
 +
it is possible to find an element $  a _ {j}  ^ {(} 2) $
 +
such that
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446026.png" /></td> </tr></table>
+
$$
 +
= a _ {1}  ^ {(} 1) \oplus \dots \oplus a _ {i-} 1  ^ {(} 1) \oplus
 +
a _ {j}  ^ {(} 2) \oplus a _ {i+} 1  ^ {(} 1) \oplus \dots \oplus a _ {m _ {1}  }
 +
^ {(} 1) ,
 +
$$
  
[[#References|[3]]], [[#References|[6]]]. In the case of completely modular lattices (cf. also [[Complete Dedekind lattice|Complete Dedekind lattice]]), which must satisfy certain additional requirements, the theorems on independent elements and direct decompositions may be applied to infinite sets as well [[#References|[4]]], [[#References|[5]]]. Complemented modular lattices have been studied; these are modular lattices with a 0 and a 1 in which for each element <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446027.png" /> there exists at least one element <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446028.png" /> (said to be a complement of the element <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446029.png" />) such that <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446030.png" />, <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446031.png" />. A complemented modular lattice which has a composition sequence, is isomorphic to the modular lattice of all subspaces of a finite-dimensional linear space over some skew-field. A complemented completely modular lattice <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446032.png" /> is isomorphic to the modular lattice of all subspaces of a linear (not necessarily finite-dimensional) space over some skew-field if and only if the following conditions are met: a) if <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446033.png" />, it is possible to find an [[Atom|atom]] <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446034.png" />; b) if <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446035.png" /> is an atom and <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446036.png" />, where <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446037.png" />, then <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446038.png" /> for some finite set <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446039.png" />; c) if <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446040.png" /> are distinct atoms, it is possible to find a third atom <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446041.png" />; and d) there exist at least three independent atoms. The last condition d) may be replaced by the requirement that the [[Desargues assumption|Desargues assumption]] be valid [[#References|[2]]]. A further generalization of this result, which leads to regular rings [[#References|[7]]], [[#References|[5]]], is connected with the theory of von Neumann algebras. For a modular lattice with a composition sequence the presence of complements is equivalent to the representability of the unit as a sum of atoms.
+
[[#References|[3]]], [[#References|[6]]]. In the case of completely modular lattices (cf. also [[Complete Dedekind lattice|Complete Dedekind lattice]]), which must satisfy certain additional requirements, the theorems on independent elements and direct decompositions may be applied to infinite sets as well [[#References|[4]]], [[#References|[5]]]. Complemented modular lattices have been studied; these are modular lattices with a 0 and a 1 in which for each element $  x $
 +
there exists at least one element $  y $(
 +
said to be a complement of the element $  x $)  
 +
such that $  x + y = 1 $,  
 +
$  xy = 0 $.  
 +
A complemented modular lattice which has a composition sequence, is isomorphic to the modular lattice of all subspaces of a finite-dimensional linear space over some skew-field. A complemented completely modular lattice $  L $
 +
is isomorphic to the modular lattice of all subspaces of a linear (not necessarily finite-dimensional) space over some skew-field if and only if the following conditions are met: a) if 0 \neq a \in L $,  
 +
it is possible to find an [[Atom|atom]] $  p \leq  a $;  
 +
b) if $  p $
 +
is an atom and $  p \leq  \sup  A $,  
 +
where $  A \subseteq L $,  
 +
then $  p \leq  \sup  F $
 +
for some finite set $  F \subseteq A $;  
 +
c) if $  p , q $
 +
are distinct atoms, it is possible to find a third atom $  r \leq  p+ q $;  
 +
and d) there exist at least three independent atoms. The last condition d) may be replaced by the requirement that the [[Desargues assumption|Desargues assumption]] be valid [[#References|[2]]]. A further generalization of this result, which leads to regular rings [[#References|[7]]], [[#References|[5]]], is connected with the theory of von Neumann algebras. For a modular lattice with a composition sequence the presence of complements is equivalent to the representability of the unit as a sum of atoms.
  
 
Modular lattices are (in the Soviet Union) also called Dedekind lattices, in honour of R. Dedekind, who was the first to formulate the modular law and established a number of its consequences [[#References|[1]]].
 
Modular lattices are (in the Soviet Union) also called Dedekind lattices, in honour of R. Dedekind, who was the first to formulate the modular law and established a number of its consequences [[#References|[1]]].
Line 23: Line 84:
 
====References====
 
====References====
 
<table><TR><TD valign="top">[1]</TD> <TD valign="top">  R. Dedekind,  "Ueber die von drei Moduln erzeugte Dualgruppe"  ''Math. Ann.'' , '''53'''  (1900)  pp. 371–403</TD></TR><TR><TD valign="top">[2]</TD> <TD valign="top">  R. Baer,  "Linear algebra and projective geometry" , Acad. Press  (1952)</TD></TR><TR><TD valign="top">[3]</TD> <TD valign="top">  G. Birkhoff,  "Lattice theory" , ''Colloq. Publ.'' , '''25''' , Amer. Math. Soc.  (1973)</TD></TR><TR><TD valign="top">[4]</TD> <TD valign="top">  A.G. Kurosh,  "The theory of groups" , '''1–2''' , Chelsea  (1955–1956)  (Translated from Russian)</TD></TR><TR><TD valign="top">[5]</TD> <TD valign="top">  L.A. Skornyakov,  "Complemented modular lattices and regular rings" , Oliver &amp; Boyd  (1964)  (Translated from Russian)</TD></TR><TR><TD valign="top">[6]</TD> <TD valign="top">  L.A. Skornyakov,  "Elements of lattice theory" , Hindushtan Publ. Comp.  (1977)  (Translated from Russian)</TD></TR><TR><TD valign="top">[7]</TD> <TD valign="top">  J. von Neumann,  "Continuous geometry" , Princeton Univ. Press  (1960)</TD></TR></table>
 
<table><TR><TD valign="top">[1]</TD> <TD valign="top">  R. Dedekind,  "Ueber die von drei Moduln erzeugte Dualgruppe"  ''Math. Ann.'' , '''53'''  (1900)  pp. 371–403</TD></TR><TR><TD valign="top">[2]</TD> <TD valign="top">  R. Baer,  "Linear algebra and projective geometry" , Acad. Press  (1952)</TD></TR><TR><TD valign="top">[3]</TD> <TD valign="top">  G. Birkhoff,  "Lattice theory" , ''Colloq. Publ.'' , '''25''' , Amer. Math. Soc.  (1973)</TD></TR><TR><TD valign="top">[4]</TD> <TD valign="top">  A.G. Kurosh,  "The theory of groups" , '''1–2''' , Chelsea  (1955–1956)  (Translated from Russian)</TD></TR><TR><TD valign="top">[5]</TD> <TD valign="top">  L.A. Skornyakov,  "Complemented modular lattices and regular rings" , Oliver &amp; Boyd  (1964)  (Translated from Russian)</TD></TR><TR><TD valign="top">[6]</TD> <TD valign="top">  L.A. Skornyakov,  "Elements of lattice theory" , Hindushtan Publ. Comp.  (1977)  (Translated from Russian)</TD></TR><TR><TD valign="top">[7]</TD> <TD valign="top">  J. von Neumann,  "Continuous geometry" , Princeton Univ. Press  (1960)</TD></TR></table>
 
 
  
 
====Comments====
 
====Comments====
 
Modular lattices satisfying the [[Desargues assumption]] are called Desarguesian lattices. Complemented completely modular lattices satisfying the identity
 
Modular lattices satisfying the [[Desargues assumption]] are called Desarguesian lattices. Complemented completely modular lattices satisfying the identity
  
<table class="eq" style="width:100%;"> <tr><td valign="top" style="width:94%;text-align:center;"><img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446042.png" /></td> </tr></table>
+
$$
 +
a \sum _ {i \in I } b _ {i}  = \
 +
\sum _ {i \in I } a b _ {i}  $$
  
whenever the set <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/m/m064/m064460/m06446043.png" /> is (upwards) directed, and the dual of the latter condition, are called continuous geometries [[#References|[5]]], [[#References|[7]]].
+
whenever the set $  \{ {b _ {i} } : {i \in I } \} $
 +
is (upwards) directed, and the dual of the latter condition, are called continuous geometries [[#References|[5]]], [[#References|[7]]].
  
 
The "dimension" is also called ''rank'', cf [[Rank of a partially ordered set]]; a "prime" interval is an [[elementary interval]].
 
The "dimension" is also called ''rank'', cf [[Rank of a partially ordered set]]; a "prime" interval is an [[elementary interval]].

Latest revision as of 08:01, 6 June 2020


Dedekind lattice

A lattice in which the modular law is valid, i.e. if $ a \leq c $, then $ ( a + b ) c = a + bc $ for any $ b $. This requirement amounts to saying that the identity $ ( ac + b ) c = ac + bc $ is valid. Examples of modular lattices include the lattices of subspaces of a linear space, of normal subgroups (but not all subgroups) of a group, of ideals in a ring, etc. A lattice with a composition sequence is a modular lattice if and only if there exists on it a dimension function $ d $, i.e. an integer-valued function such that $ d ( x + y ) + d ( xy ) = d ( x ) + d ( y ) $ and such that if the interval $ [ a , b] $ is prime, it follows that $ d ( b ) = d ( a ) + 1 $. If $ w = a _ {1} ^ {(} 1) \dots a _ {m _ {1} } ^ {(} 1) = a _ {1} ^ {(} 2) \dots a _ {m _ {2} } ^ {(} 2) $, if none of the elements $ a _ {i} ^ {(} k) $ can be represented as a product of elements other than itself and if

$$ a _ {1} ^ {(} k) \dots a _ {i-} 1 ^ {(} k) a _ {i+} 1 ^ {(} k) \dots a _ {mk} ^ {(} k) \Nle a _ {i} ^ {(} k) , $$

then $ m _ {1} = m _ {2} $ and for any $ a _ {i} ^ {(} 1) $ it is possible to find an element $ a _ {j} ^ {(} 2) $ such that

$$ w = a _ {1} ^ {(} 1) \dots a _ {i-} 1 ^ {(} 1) a _ {j} ^ {(} 2) a _ {i+} 1 ^ {(} 1) \dots a _ {m _ {1} } ^ {(} 1) , $$

[3], [6]. Non-zero elements $ a _ {1} \dots a _ {n} $ of a modular lattice with a zero 0 are said to be independent if $ ( a _ {1} + \dots + a _ {i-} 1 + a _ {j+} 1 + \dots + a _ {n} ) a _ {i} = 0 $ for all $ i $. This definition makes it possible to generalize many properties of systems of linearly independent vectors [3], [5], [6]. If $ a _ {1} \dots a _ {n} $ are independent, their sum is denoted by $ a _ {1} \oplus \dots \oplus a _ {n} $. Ore's theorem: If a modular lattice has a composition sequence and if

$$ 1 = a _ {1} ^ {(} 1) \oplus \dots \oplus a _ {m _ {1} } ^ {(} 1) = \ a _ {1} ^ {(} 2) \oplus \dots \oplus a _ {m _ {2} } ^ {(} 2) , $$

none of the elements $ a _ {i} ^ {(} k) $ being representable as a sum of two independent elements, then $ m _ {1} = m _ {2} $ and for each $ a _ {i} ^ {(} 1) $ it is possible to find an element $ a _ {j} ^ {(} 2) $ such that

$$ 1 = a _ {1} ^ {(} 1) \oplus \dots \oplus a _ {i-} 1 ^ {(} 1) \oplus a _ {j} ^ {(} 2) \oplus a _ {i+} 1 ^ {(} 1) \oplus \dots \oplus a _ {m _ {1} } ^ {(} 1) , $$

[3], [6]. In the case of completely modular lattices (cf. also Complete Dedekind lattice), which must satisfy certain additional requirements, the theorems on independent elements and direct decompositions may be applied to infinite sets as well [4], [5]. Complemented modular lattices have been studied; these are modular lattices with a 0 and a 1 in which for each element $ x $ there exists at least one element $ y $( said to be a complement of the element $ x $) such that $ x + y = 1 $, $ xy = 0 $. A complemented modular lattice which has a composition sequence, is isomorphic to the modular lattice of all subspaces of a finite-dimensional linear space over some skew-field. A complemented completely modular lattice $ L $ is isomorphic to the modular lattice of all subspaces of a linear (not necessarily finite-dimensional) space over some skew-field if and only if the following conditions are met: a) if $ 0 \neq a \in L $, it is possible to find an atom $ p \leq a $; b) if $ p $ is an atom and $ p \leq \sup A $, where $ A \subseteq L $, then $ p \leq \sup F $ for some finite set $ F \subseteq A $; c) if $ p , q $ are distinct atoms, it is possible to find a third atom $ r \leq p+ q $; and d) there exist at least three independent atoms. The last condition d) may be replaced by the requirement that the Desargues assumption be valid [2]. A further generalization of this result, which leads to regular rings [7], [5], is connected with the theory of von Neumann algebras. For a modular lattice with a composition sequence the presence of complements is equivalent to the representability of the unit as a sum of atoms.

Modular lattices are (in the Soviet Union) also called Dedekind lattices, in honour of R. Dedekind, who was the first to formulate the modular law and established a number of its consequences [1].

References

[1] R. Dedekind, "Ueber die von drei Moduln erzeugte Dualgruppe" Math. Ann. , 53 (1900) pp. 371–403
[2] R. Baer, "Linear algebra and projective geometry" , Acad. Press (1952)
[3] G. Birkhoff, "Lattice theory" , Colloq. Publ. , 25 , Amer. Math. Soc. (1973)
[4] A.G. Kurosh, "The theory of groups" , 1–2 , Chelsea (1955–1956) (Translated from Russian)
[5] L.A. Skornyakov, "Complemented modular lattices and regular rings" , Oliver & Boyd (1964) (Translated from Russian)
[6] L.A. Skornyakov, "Elements of lattice theory" , Hindushtan Publ. Comp. (1977) (Translated from Russian)
[7] J. von Neumann, "Continuous geometry" , Princeton Univ. Press (1960)

Comments

Modular lattices satisfying the Desargues assumption are called Desarguesian lattices. Complemented completely modular lattices satisfying the identity

$$ a \sum _ {i \in I } b _ {i} = \ \sum _ {i \in I } a b _ {i} $$

whenever the set $ \{ {b _ {i} } : {i \in I } \} $ is (upwards) directed, and the dual of the latter condition, are called continuous geometries [5], [7].

The "dimension" is also called rank, cf Rank of a partially ordered set; a "prime" interval is an elementary interval.

How to Cite This Entry:
Modular lattice. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Modular_lattice&oldid=38978
This article was adapted from an original article by L.A. Skornyakov (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article