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In [[mathematics]], the '''Littlewood–Richardson rule''' is a combinatorial description of the coefficients that arise when decomposing a product of two [[Schur polynomial|Schur functions]] as a linear combination of other Schur functions. These coefficients are natural numbers, which the Littlewood–Richardson rule describes as counting certain [[skew tableau]]x. They occur in many other mathematical contexts, for instance as [[Multiplicity (mathematics)|multiplicity]] in the decomposition of [[tensor product]]s of [[irreducible representation]]s of [[general linear group]]s (or related groups like the [[special linear group|special linear]] and [[special unitary group]]s), or in the decomposition of certain [[induced representations]] in the [[representation theory of the symmetric group]], or in the area of [[algebraic combinatorics]] dealing with [[Young tableaux]] and [[symmetric polynomials]].

Littlewood–Richardson coefficients depend on three [[integer partition|partition]]s, say <math>\lambda,\mu,\nu</math>, of which <math>\lambda</math> and <math>\mu</math> describe the Schur functions being multiplied, and <math>\nu</math> gives the Schur function of which this is the coefficient in the linear combination; in other words they are the coefficients <math>c_{\lambda,\mu}^\nu</math> such that
:<math>s_\lambda s_\mu=\sum_\nu c_{\lambda,\mu}^\nu s_\nu.</math>
The Littlewood–Richardson rule states that <math>c_{\lambda,\mu}^\nu</math> is equal to the number of Littlewood–Richardson tableaux of [[Skew tableau|skew shape]] <math>\nu/\lambda</math> and of weight <math>\mu</math>.

== History ==

{{quote box
|align=right
|width=33%
|quote=Unfortunately the Littlewood–Richardson rule is much harder to prove than was at first suspected. The author was once told that the Littlewood–Richardson rule helped to get men on the moon but was not proved until after they got there. 
|source={{harvs|txt|first=Gordon|last=James|year=1987}}
}}
The Littlewood–Richardson rule by {{harvs|txt|author1-link=Dudley E. Littlewood|author2-link=Archibald Read Richardson|year= 1934|last=Littlewood |first=D. E.|last2= Richardson |first2=A. R.|loc=theorem III p. 119}} but though they claimed it as a theorem they only proved it in some fairly simple special cases. 
{{harvs|txt|authorlink=Gilbert de Beauregard Robinson|last=Robinson|year=1938}} claimed to complete their proof, but his argument had gaps, though it was so obscurely written that these gaps were not noticed for some time, and his argument is reproduced in the book  {{harv|Littlewood|1950}}. Some of the gaps were later filled by {{harvtxt|Macdonald|1995}}. The first rigorous proofs of the rule were given four decades after it was found, by {{harvs|txt|last=Schützenberger|year1=1977}} and {{harvtxt|Thomas|1974}}, after the necessary combinatorial theory was developed by {{harvs|txt|authorlink=Craige Schensted|last=Schensted|first= C.|year=1961}}, {{harvs|txt|last=Schützenberger|year1=1963}}, and {{harvs|txt|authorlink=Donald Knuth|last=Knuth|year=1970}} in their work on the [[Robinson–Schensted correspondence]]. 
There are now several short proofs of the rule, such as {{harv|Gasharov|1998}},  and {{harv|Stembridge|2002}} using [[Bender-Knuth involution]]s.
{{harvtxt|Littelmann|1994}} used the  [[Littelmann path model]] to generalize the Littlewood–Richardson rule to other semisimple Lie  groups.

The Littlewood–Richardson rule is notorious for the number of errors that appeared prior to its complete, published proof. Several published attempts to prove it are incomplete, and it is particularly difficult to avoid errors when doing hand calculations with it: even the original example in {{harvs|txt|year= 1934|last=Littlewood |first=D. E.|last2= Richardson |first2=A. R.}} contains an error.

The Littlewood–Richardson rule states that <math>c_{\lambda,\mu}^\nu</math> is equal to the number of Littlewood–Richardson tableaux of shape <math>\nu/\lambda</math> and of weight <math>\mu</math>.

=== Littlewood–Richardson tableaux ===

[[Image:LR tableau of shape (4,3,2)-(2,1) word 112123.svg|thumb|right||A Littlewood–Richardson tableau]]
A Littlewood–Richardson tableau is a skew [[Young tableau#Definitions|semistandard tableau]] with the additional property that the sequence obtained by concatenating its reversed rows is a lattice word (or lattice permutation), which means that in every initial part of the sequence any number <math>i</math> occurs at least as often as the number <math>i+1</math>. Another equivalent (though not quite obviously so) characterization is that the tableau itself, and any tableau obtained from it by removing some number of its leftmost columns, has a weakly decreasing weight. Many other combinatorial notions have been found that turn out to be in bijection with Littlewood–Richardson tableaux, and can therefore also be used to define the Littlewood–Richardson coefficients.

[[Image:LR tableau of shape (4,3,2)-(2,1) word 112213.svg|thumb|right||Another Littlewood–Richardson tableau]]

=== Example ===

Consider the case that <math>\lambda=(2,1)</math>, <math>\mu=(3,2,1)</math> and <math>\nu=(4,3,2)</math>. Then the fact that <math>c_{\lambda,\mu}^\nu=2</math> can be deduced from the fact that the two tableaux shown at the right are the only two Littlewood–Richardson tableaux of shape <math>\nu/\lambda</math> and weight <math>\mu</math>. Indeed, since the last box on the first nonempty line of the skew diagram can only contain an entry 1, the entire first line must be filled with entries 1 (this is true for any Littlewood–Richardson tableau); in the last box of the second row we can only place a 2 by column strictness and the fact that our lattice word cannot contain any larger entry before it contains a 2. For the first box of the second row we can now either use a 1 or a 2. Once that entry is chosen, the third row must contain the remaining entries to make the weight (3,2,1), in a weakly increasing order, so we have no choice left any more; in both case it turns out that we do find a Littlewood–Richardson tableau.

=== A more geometrical description ===

The condition that the sequence of entries read from the tableau in a somewhat peculiar order form a lattice word, can be replaced by a more local and geometrical condition. Since in a semistandard tableau equal entries never occur in the same column, one can number the copies of any value from right to left, which is their order in of occurrence in the sequence that should be a lattice word. Call the number so associated to each entry its index, and write an entry ''i'' with index ''j'' as ''i''[''j'']. Now if some Littlewood–Richardson tableau contains an entry <math>i>1</math> occurs with index ''j'', then that entry ''i''[''j''] should occur in a row strictly below that of <math>i-1[j]</math> (which certainly also occurs, since the entry ''i''&nbsp;−&nbsp;1 occurs as least as often as the entry ''i'' does). In fact the entry ''i''[''j''] should also occur in a column no further to the right than that same entry <math>i-1[j]</math> (which at first sight appears to be a stricter condition). If the weight of the Littlewood–Richardson tableau is fixed beforehand, then one can form a fixed collection of indexed entries, and the if these are placed in a way respecting those geometric restrictions, in addition to those of [[Young tableau#Definitions|semistandard tableaux]] and the condition that indexed copies of the same entries should respect right-to-left ordering of the indexes, then the resulting tableaux are guaranteed to be Littlewood–Richardson tableaux.

== An algorithmic form of the rule ==

The Littlewood–Richardson as stated above gives a combinatorial expression for individual Littlewood–Richardson coefficients, but gives no indication of a practical method to enumerate the Littlewood–Richardson tableaux in order to find the values of these coefficients. Indeed for given <math>\lambda,\mu,\nu</math> there is no simple criterion to determine whether any Littlewood–Richardson tableaux of shape <math>\nu/\lambda</math> and of weight <math>\mu</math> exist at all (although there are a number of necessary conditions, the simplest of which is <math>|\lambda|+|\mu|=|\nu|</math>); therefore it seems inevitable that in some cases one has to go through an elaborate search, only to find that no solutions exist.

Nevertheless, the rule leads to a quite efficient procedure to determine the full decomposition of a product of Schur functions, in other words to determine all coefficients <math>c_{\lambda,\mu}^\nu</math> for fixed λ and μ, but varying ν. This fixes the weight of the Littlewood–Richardson tableaux to be constructed and the "inner part" λ of their shape, but leaves the "outer part" ν free. Since the weight is known, the set of indexed entries in the geometric description is fixed. Now for successive indexed entries, all possible positions allowed by the geometric restrictions can be tried in a [[backtracking]] search. The entries can be tried in increasing order, while among equal entries they can be tried by ''decreasing'' index. The latter point is the key to efficiency of the search procedure: the entry ''i''[''j''] is then restricted to be in a column to the right of <math>i[j+1]</math>, but no further to the right than <math>i-1[j]</math> (if such entries are present). This strongly restricts the set of possible positions, but ''always leaves at least one valid position for <math>i[j]</math>''; thus every placement of an entry will give rise to at least one complete Littlewood–Richardson tableau, and the [[search tree]] contains no dead ends.

A similar method can be used to find  all coefficients <math>c_{\lambda,\mu}^\nu</math> for fixed λ and ν, but varying μ.

==Littlewood–Richardson coefficients==

The Littlewood–Richardson coefficients ''c''{{sup sub|ν|λμ}}&nbsp;&nbsp;  appear in the following ways:
*They are the structure constants for the product in the [[ring of symmetric functions]] with respect to the basis of Schur functions
:<math>s_\lambda s_\mu =\sum c_{\lambda\mu}^\nu s_\nu</math>
:or equivalently ''c''{{sup sub|ν|λμ}}&nbsp;&nbsp; is the inner product of ''s''<sub>&nu;</sub> and ''s''<sub>&lambda;</sub>''s''<sub>&mu;</sub>.
*They express [[skew Schur function]]s in terms of Schur functions
:<math>s_{\nu/\lambda} =\sum _\mu c_{\lambda\mu}^\nu s_\mu.</math>
*The ''c''{{sup sub|ν|λμ}}&nbsp;&nbsp;    appear as intersection numbers on a [[Grassmannian]]:
:<math>\sigma_\lambda \sigma_\mu =\sum c_{\lambda\mu}^\nu \sigma_\nu</math>
:where &sigma;<sub>μ</sub> is the class of the [[Schubert variety]] of a Grassmannian corresponding to μ.
*''c''{{sup sub|ν|λμ}}&nbsp;&nbsp;  is the number of times the irreducible representation ''V''<sub>&lambda;</sub> &otimes; ''V''<sub>&mu;</sub> of the product of symmetric groups ''S''<sub>|&lambda;|</sub> &times; ''S''<sub>|&mu;|</sub> appears in the restriction of the representation ''V''<sub>&nu;</sub> of ''S''<sub>|&nu;|</sub> to ''S''<sub>|&lambda;|</sub> &times; ''S''<sub>|&mu;|</sub>. By [[Frobenius reciprocity]] this is also the number of times that ''V''<sub>&nu;</sub> occurs in the representation of ''S''<sub>|&nu;|</sub> induced from ''V''<sub>&lambda;</sub> &otimes; ''V''<sub>&mu;</sub>.
*The ''c''{{sup sub|ν|λμ}}&nbsp;&nbsp;    appear in the decomposition of the tensor product {{harv|Fulton|1997}} of two [[Schur module]]s (irreducible representations of special linear groups)
:<math>E^\lambda \otimes E^\mu =\bigoplus_\nu (E^\nu)^{\oplus c_{\lambda\mu}^\nu}.</math>
*''c''{{sup sub|ν|λμ}}&nbsp;&nbsp;  is the number of standard Young tableaux of shape &nu;/&mu; that are [[jeu de taquin]] equivalent to some fixed standard Young tableau of shape &lambda;.
*''c''{{sup sub|ν|λμ}}&nbsp;&nbsp; is the number of Littlewood–Richardson tableaux of shape ν/λ and of weight μ.
*''c''{{sup sub|ν|λμ}}&nbsp;&nbsp; is the number of [[picture (mathematics)|pictures]] between μ and ν/λ.

==Generalizations and special cases==
{{harvtxt|Zelevinsky|1981}} extended the Littlewood–Richardson rule to skew Schur functions as follows:
:<math>s_\lambda s_{\mu/\nu} = \sum_{\lambda+\omega(T_{\ge j})\in P}s_{\lambda+\omega(T)}</math>
where the sum is over all tableaux ''T'' on &mu;/&nu; such that for all ''j'', the sequence of integers &lambda;+&omega;(''T''<sub>&ge;''j''</sub>) is non-increasing, and &omega; is the weight.

[[Pieri's formula]], which is the special case of the Littlewood–Richardson rule in the case when one of the partitions has only '''one part''', states that 
*<math>\displaystyle S_\mu S_n=\sum_\lambda S_\lambda</math>
where ''S''<sub>''n''</sub> is the Schur function of a partition with one row and the sum is over all partitions &lambda; obtained from &mu; by adding ''n'' elements to its [[Ferrers diagram]], no two in the same column.

If both partitions are '''rectangular''' in shape, the sum is also multiplicity free {{harv|Okada|1998}}. Fix ''a'', ''b'', ''p'', and ''q'' positive integers with ''p'' <math>\geq</math> ''q''. Denote by <math>(a^p)</math> the partition with ''p'' parts of length ''a''. The partitions indexing nontrivial components of <math>s_{(a^p)}s_{(b^q)}</math> are those partitions <math>\lambda</math> with length <math>\leq p+q</math> such that 
*<math>\lambda_{q+1} = \lambda_{q+2} = \cdots = \lambda_p = a,</math>
*<math>\lambda_q \geq \mathrm{max}(a,b)</math>
*<math>\lambda_i + \lambda_{p+q - i + 1} = a+b, \quad {i = 1, \dots, q}.</math>
For example,
[[File:Schur functions rectangular example.png|center|400px]].

==Examples==

The examples of Littlewood-Richardson coefficients below are given in terms of products of Schur polynomials ''S''<sub>&pi;</sub>, indexed by partitions &pi;, using the formula 
:<math>S_\lambda S_\mu =\sum c_{\lambda\mu}^\nu S_\nu.</math>

All coefficients with &nu; at most 4 are given by:
*''S''<sub>0</sub>''S''<sub>&pi;</sub> = ''S''<sub>&pi;</sub> for any &pi;. where ''S''<sub>0</sub>=1 is the Schur polynomial of the empty partition
*''S''<sub>1</sub>''S''<sub>1</sub> = ''S''<sub>2</sub> + ''S''<sub>11</sub>
*''S''<sub>2</sub>''S''<sub>1</sub> = ''S''<sub>3</sub> + ''S''<sub>21</sub>
*''S''<sub>11</sub>''S''<sub>1</sub> = ''S''<sub>111</sub> + ''S''<sub>21</sub>
*''S''<sub>3</sub>''S''<sub>1</sub> = ''S''<sub>4</sub> + ''S''<sub>31</sub>
*''S''<sub>21</sub>''S''<sub>1</sub> = ''S''<sub>31</sub> + ''S''<sub>22</sub> + ''S''<sub>211</sub>
*''S''<sub>2</sub>''S''<sub>2</sub> = ''S''<sub>4</sub> + ''S''<sub>31</sub> + ''S''<sub>22</sub>
*''S''<sub>2</sub>''S''<sub>11</sub> = ''S''<sub>31</sub> + ''S''<sub>211</sub>
*''S''<sub>111</sub>''S''<sub>1</sub> = ''S''<sub>1111</sub> + ''S''<sub>211</sub>
*''S''<sub>11</sub>''S''<sub>11</sub> = ''S''<sub>1111</sub> + ''S''<sub>211</sub> + ''S''<sub>22</sub>

Most of the coefficients for small partitions are 0 or 1, which happens in particular whenever one of the factors is of the form ''S<sub>n</sub>'' or ''S''<sub>11...1</sub>, because of [[Pieri's formula]] and its transposed counterpart. The simplest example with a coefficient larger than 1 happens when neither of the factors has this form:
*''S''<sub>21</sub>''S''<sub>21</sub> = ''S''<sub>42</sub> + ''S''<sub>411</sub> + ''S''<sub>33</sub> + 2''S''<sub>321</sub> + ''S''<sub>3111</sub> + ''S''<sub>222</sub> + ''S''<sub>2211</sub>.
For larger partitions the coefficients become more complicated. For example,
*''S''<sub>321</sub>''S''<sub>321</sub> = ''S''<sub>642</sub> +''S''<sub>6411</sub> +''S''<sub>633</sub> +2''S''<sub>6321</sub> +''S''<sub>63111</sub> +''S''<sub>6222</sub> +''S''<sub>62211</sub> +''S''<sub>552</sub> +''S''<sub>5511</sub> +2''S''<sub>543</sub> +4''S''<sub>5421</sub> +2''S''<sub>54111</sub>  +3''S''<sub>5331</sub> +3''S''<sub>5322</sub> +4''S''<sub>53211</sub> +''S''<sub>531111</sub> +2''S''<sub>52221</sub> +''S''<sub>522111</sub> +''S''<sub>444</sub> +3''S''<sub>4431</sub> +2''S''<sub>4422</sub> +3''S''<sub>44211</sub> +''S''<sub>441111</sub> +3''S''<sub>4332</sub> +3''S''<sub>43311</sub> +4''S''<sub>43221</sub> +2''S''<sub>432111</sub> +''S''<sub>42222</sub> +''S''<sub>422211</sub> +''S''<sub>3333</sub> +2''S''<sub>33321</sub> +''S''<sub>333111</sub> +''S''<sub>33222</sub> +''S''<sub>332211</sub> with 34  terms and total multiplicity 62, and the largest coefficient is 4
*''S''<sub>4321</sub>''S''<sub>4321</sub> is a sum of 206  terms with total multiplicity is 930, and the largest coefficient is 18.
*''S''<sub>54321</sub>''S''<sub>54321</sub> is a sum of 1433  terms with total multiplicity  26704, and the largest coefficient (that of ''S''<sub>86543211</sub>) is 176.
*''S''<sub>654321</sub>''S''<sub>654321</sub> is a sum of 10873 terms with total multiplicity is 1458444 (so the average value of the coefficients is more than 100, and they can be as large as 2064).

The original example given by {{harvtxt|Littlewood|Richardson|1934|loc=p. 122-124}} was (after correcting for 3 tableaux they found but forgot to include in the final sum) 
*''S''<sub>431</sub>''S''<sub>221</sub> =  ''S''<sub>652</sub> + ''S''<sub>6511</sub>  + ''S''<sub>643</sub> + 2''S''<sub>6421</sub> + ''S''<sub>64111</sub> + ''S''<sub>6331</sub> + ''S''<sub>6322</sub> + ''S''<sub>63211</sub> + ''S''<sub>553</sub> + 2''S''<sub>5521</sub> + ''S''<sub>55111</sub> + 2''S''<sub>5431</sub> + 2''S''<sub>5422</sub> + 3''S''<sub>54211</sub>  + ''S''<sub>541111</sub> + ''S''<sub>5332</sub> + ''S''<sub>53311</sub> + 2''S''<sub>53221</sub> + ''S''<sub>532111</sub> + ''S''<sub>4432</sub> + ''S''<sub>44311</sub> + 2''S''<sub>44221</sub> + ''S''<sub>442111</sub> + ''S''<sub>43321</sub> + ''S''<sub>43222</sub> + ''S''<sub>432211</sub>
with 26 terms coming from the following 34 tableaux:

<pre>
....11 ....11 ....11 ....11 ....11 ....11 ....11 ....11 ....11    
...22  ...22  ...2   ...2   ...2   ...2   ...    ...    ...
.3     .      .23    .2     .3     .      .22    .2     .2     
       3             3      2      2      3      23     2      
                                   3                    3

....1  ....1  ....1  ....1  ....1  ....1  ....1  ....1  ....1   
...12  ...12  ...12  ...12  ...1   ...1   ...1   ...2   ...1
.23    .2     .3     .      .23    .22    .2     .1     .2      
       3      2      2      2      3      23     23     2
                     3                                  3      

....1  ....1  ....1  ....1  ....1  ....1  ....1  ....1   
...2   ...2   ...2   ...    ...    ...    ...    ...    
.1     .3     .      .12    .12    .1     .2     .2      
2      1      1      23     2      22     13     1
3      2      2             3      3      2      2
              3                                  3

....   ....   ....   ....   ....   ....   ....   ....   
...1   ...1   ...1   ...1   ...1   ...    ...    ...    
.12    .12    .1     .2     .2     .11    .1     .1      
23     2      22     13     1      22     12     12
       3      3      2      2      3      23     2
                            3                    3
</pre>

Calculating skew Schur functions is similar. 
For example, the 15 Littlewood–Richardson tableaux for ν=5432 and λ=331 are 
<pre>
...11 ...11 ...11 ...11 ...11 ...11 ...11 ...11 ...11 ...11 ...11 ...11 ...11 ...11 ...11
...2  ...2  ...2  ...2  ...2  ...2  ...2  ...2  ...2  ...2  ...2  ...2  ...2  ...2  ...2
.11   .11   .11   .12   .11   .12   .13   .13   .23   .13   .13   .12   .12   .23   .23
12    13    22    12    23    13    12    24    14    14    22    23    33    13    34
</pre>
so ''S''<sub>5432/331</sub> = &Sigma;''c''{{sup sub|ν|λμ}}&nbsp;&nbsp;''S''<sub>μ</sub> = ''S''<sub>52</sub> + ''S''<sub>511</sub> + ''S''<sub>4111</sub> + ''S''<sub>2221</sub> + 2''S''<sub>43</sub> + 2''S''<sub>3211</sub> + 2''S''<sub>322</sub> + 2''S''<sub>331</sub> + 3''S''<sub>421</sub> {{harv|Fulton|1997|p=64}}.

== References ==
*{{Citation | last1=Fulton | first1=William | author1-link=William Fulton (mathematician) | title=Young tableaux | publisher=[[Cambridge University Press]] | series=London Mathematical Society Student Texts | isbn=978-0-521-56144-0; 978-0-521-56724-4 | id={{MathSciNet | id = 1464693}} | year=1997 | volume=35 | page=121}}
*{{Citation | last1=Gasharov | first1=Vesselin | title=A short proof of the Littlewood-Richardson rule | doi=10.1006/eujc.1998.0212     | id={{MathSciNet | id = 1630540}} | year=1998 | journal=European Journal of Combinatorics | issn=0195-6698 | volume=19 | issue=4 | pages=451–453 | url=http://www.math.cornell.edu/~vesko/papers/lrrule.ps }}
*{{Citation | last1=James | first1=Gordon | title=The Arcata Conference on Representations of Finite Groups (Arcata, Calif., 1986) | publisher=[[American Mathematical Society]] | location=Providence, R.I. | series=Proc. Sympos. Pure Math. | id={{MathSciNet | id = 933355}} | year=1987 | volume=47 | chapter=The representation theory of the symmetric groups | pages=111–126}}
*{{Citation | last1=Knuth | first1=Donald E. | author1-link=Donald Knuth | title=Permutations, matrices, and generalized Young tableaux | url=http://projecteuclid.org/euclid.pjm/1102971948 | id={{MathSciNet | id = 0272654}} | year=1970 | journal=[[Pacific Journal of Mathematics]] | issn=0030-8730 | volume=34 | pages=709–727}}
*{{citation|last=Littelmann|first=Peter|title=A Littlewood-Richardson rule for symmetrizable Kac-Moody algebras|journal= Invent. Math.|volume= 116|year=1994|pages=329–346|doi=10.1007/BF01231564 |url=http://www.mi.uni-koeln.de/~littelma/papers/Inventmath.pdf}}
*{{Citation | last1=Littlewood | first1=Dudley E. | title=The theory of group characters and matrix representations of groups | url=http://www.ams.org/bookstore?fn=20&arg1=alggeom&item=CHEL-357-H | publisher=AMS Chelsea Publishing, Providence, RI | isbn=978-0-8218-4067-2 | id={{MathSciNet | id = 00002127}} | year=1950}}
*{{Citation | last1=Littlewood | first1=D. E. | last2=Richardson | first2=A. R. | title=Group Characters and Algebra | url=http://www.jstor.org/stable/91293 | publisher=The Royal Society | year=1934 | journal=Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character | issn=0264-3952 | volume=233 | pages=99–141 | doi=10.1098/rsta.1934.0015 | issue=721–730}}
*{{Citation | last1=Macdonald | first1=I. G. | author1-link=Ian G. Macdonald | title=Symmetric functions and Hall polynomials | url=http://www.oup.com/uk/catalogue/?ci=9780198504504 | publisher=The Clarendon Press Oxford University Press | edition=2nd | series=Oxford Mathematical Monographs | isbn=978-0-19-853489-1 | id={{MathSciNet | id = 1354144}} | year=1995}}
*{{Citation | last1=Okada | first1=Soichi | title=Applications of minor summation formulas to rectangular-shaped representations of classical groups | doi=10.1006/jabr.1997.7408 | id={{MathSciNet | id = 1632816}} | year=1998 | journal=[[Journal of Algebra]] | issn=0021-8693 | volume=205 | issue=2 | pages=337–367 | unused_data=DUPLICATE DATA: doi=10.1006/jabr.1997.7408}}
*{{Citation | last1=Robinson | first1=G. de B. | title=On the Representations of the Symmetric Group | publisher=The Johns Hopkins University Press | year=1938 | journal=[[American Journal of Mathematics]] | issn=0002-9327 | volume=60 | issue=3 | pages=745–760 | doi=10.2307/2371609 | jstor=2371609}} [[Zentralblatt MATH|Zbl]][http://www.zentralblatt-math.org/zmath/en/search/?q=an:0019.25102 0019.25102]
*{{Citation | last1=Schensted | first1=C. | title=Longest increasing and decreasing subsequences | id={{MathSciNet | id = 0121305}} | year=1961 | journal=Canadian Journal of Mathematics | issn=0008-414X | volume=13 | pages=179–191|url=http://books.google.com/?id=G3sZ2zG8AiMC | doi=10.4153/CJM-1961-015-3}}
*{{Citation | last1=Schützenberger | first1=M. P. | title=Quelques remarques sur une construction de Schensted | url=http://gdz.sub.uni-goettingen.de/no_cache/dms/load/img/?IDDOC=221996 | id={{MathSciNet | id = 0190017}} | year=1963 | journal=Mathematica Scandinavica | issn=0025-5521 | volume=12 | pages=117–128}}
*{{Citation | last1=Schützenberger | first1=Marcel-Paul | title=Combinatoire et représentation du groupe symétrique (Actes Table Ronde CNRS, Univ. Louis-Pasteur Strasbourg, Strasbourg, 1976) | publisher=[[Springer-Verlag]] | location=Berlin, New York | series=Lecture notes in mathematics | doi=10.1007/BFb0090012 | id={{MathSciNet | id = 0498826}} | year=1977 | volume=579 | chapter=La correspondance de Robinson | pages=59–113 | isbn=978-3-540-08143-2 | url=http://www-igm.univ-mlv.fr/~berstel/Mps/Travaux/A/1977-4CorrespRobinsonStrasbourg.pdf}}
*{{Citation | last1=Stembridge | first1=John R. | title=A concise proof of the Littlewood-Richardson rule | url=http://www.emis.de/journals/EJC/Volume_9/PDF/v9i1n5.pdf | id={{MathSciNet | id = 1912814}} | year=2002 | journal=Electronic Journal of Combinatorics | issn=1077-8926 | volume=9 | issue=1 | pages=Note 5, 4 pp. (electronic)}}
*{{citation|last=Thomas|first= Glânffrwd P.
|title=Baxter algebras and Schur functions|series= Ph.D. Thesis|publisher= University College of Swansea|place= Swansea|year= 1974}}
*{{Citation | last1=van Leeuwen | first1=Marc A. A. | title=Interaction of combinatorics and representation theory | url=http://www-math.univ-poitiers.fr/~maavl/pdf/lrr.pdf | publisher=Math. Soc. Japan | location=Tokyo | series=MSJ Mem. | id={{MathSciNet | id = 1862150}} | year=2001 | volume=11 | chapter=The Littlewood-Richardson rule, and related combinatorics | pages=95–145}}
*{{Citation | last1=Zelevinsky | first1=A. V. | title=A generalization of the Littlewood-Richardson rule and the Robinson-Schensted-Knuth correspondence | doi=10.1016/0021-8693(81)90128-9     | id={{MathSciNet | id = 613858}} | year=1981 | journal=Journal of Algebra | issn=0021-8693 | volume=69 | issue=1 | pages=82–94}}

== External links ==
* [http://young.sp2mi.univ-poitiers.fr/cgi-bin/form-prep/marc/LiE_form.act?action=LRR An online program], decomposing products of Schur functions using the Littlewood–Richardson rule

{{DEFAULTSORT:Littlewood-Richardson rule}}
[[Category:Algebraic combinatorics]]
[[Category:Invariant theory]]
[[Category:Representation theory]]
[[Category:Symmetric functions]]