On d-Permutations and Pattern Avoidance Classes

Multidimensional permutations, or d-permutations, are represented by their diagrams on \([n]^d\) such that there exists exactly one point per hyperplane \(x_i\) that satisfies \(x_i= j\) for \(i \in [d]\) and \(j \in [n]\). Bonichon and Morel previously enumerated 3-permutations avoiding small patterns, and we extend their results by first proving four conjectures, which exhaustively enumerate 3-permutations avoiding any two fixed patterns of size 3. We further provide a enumerative result relating 3-permutation avoidance classes with their respective recurrence relations. In particular, we show a recurrence relation for 3-permutations avoiding the patterns 132 and 213, which contributes a new sequence to the OEIS database. We then extend our results to completely enumerate 3-permutations avoiding three patterns of size 3.