The associativity of $n$-dimensional copulas in the sense of Post is studied. These copulas are shown to be just $n$-ary extensions of associative 2-dimensional copulas with special constraints, thus they solve an open problem of R. Mesiar posed during the International Conference FSTA 2010 in Liptovsk\'y J\'an, Slovakia.
Archimedean copula, associativity in the sense of Post, $n$-dimensional copula
03E72