There are exactly six pairs in D, the domain of tau, if d = 1 and P is the property Integer Distance Bounded by 2. Why six?
Answer:
D is the set of ordered pairs (x,y) such that {1,x,y} is a permissible
unordered triples for P .
The set of permissible triples is
{0,0,0} {0,1,1} {0,2,2} {1,1,1} {1,1,2} {1,2,2} {2,2,2}
Thus, D consist of the ordered pairs
(0,1) (1,0) (1,1) (1,2) (2,1) (2,2)