BPS States, Crystals, and Matrices

Figure 3

Finite pyramids with 𝑚=1,2,3 stones in the top row (resp., (a), (b), and (c)), whose generating functions are given by 𝑍^pyramid_𝑚+1 (note that 𝑍^pyramid₁=1 corresponds to an empty pyramid corresponding to the pure D6-brane).

(a)

(b)

(c)