Enumeration of States and Signals with 2 Sites.
The tabled values represent the number of sites in each category. The number of unrestricted and successful sites, Y1, is the sum of columns 2 and 4 (SE and SO). The number of occupied sites next period, S+, is the sum of columns 3 and 4 (NO and SO).
NE: either restricted or not successful/empty next period.
SE: unrestricted, successful/empty next period.
NO: either restricted or not successful/occupied next period.
SO: unrestricted, successful/occupied next period.