Tamari lattice
In mathematics, the Tamari lattice is an algebraic structure that concisely represents some of the important logical and geometric properties of associativity. More formally, the Tamari lattice of order n, introduced by Dov Tamari (1951) and sometimes notated Tn or Yn, is a partially ordered set in which the elements consist of all ways of bracketing a sequence of n+1 letters using n pairs of parentheses, with the ordering induced by only rightward applications of the associative law ((xy)z) → (x(yz)).