Hi,everyone .Let A a no-empty set ,suppose A is finite and let n ,natural \neq 0 , its cardinality ,let k a natural number \neq 0 : we say every ordinate k -upla ( a_{1}...a_{k}) is a disposition with repetition of class k of A where a_{i} \in A .To define a combination with repetition of class k of A i gave the following deinition: let ( a_{1}...a_{k}) , ( b_{1}...b_{k}) two dispositions with repetition of class k of A .We say ( a_{1}...a_{k}) and ( b_{1}...b_{k}) are "of the same type" if \{a_{1}...a_{k}\} =\{b_{1}...b_{k}\} , and ,set \{a_{1}...a_{k}\}=\{c_{1}...c_{r}\} ,where r is the cardinality of \{a_{1}...a_{k}\} , we have \forall i\in \{1,...,r\} \sharp ( \{j \in\{1,...,k\}\mid a_{j}=c_{i} \} = \sharp ( \{j \in\{1,...,k\}\mid b_{j}=c_{i} \} . So we can consider the following set R= \{ (a,b) \in \{ every disposition with repetion of class k of A \}^{2}\mid a and b are "of the same type" \} and observe R is an equivalence relation on \{ every disposition with repetiton of class k of A } ,so we can say \forall disposition with repetition of class k of A } , a , the equivalence class of a on \{ every disposition with repetition of class k of A } modulo R is a combination with repetition of class k of A .Is this definition already used ?