a(x, y) = (3 * x) + y ≤ 2
b(x, y) = (2 * x) - y ≥ -1
c(x, y) = x + y ≥ -1
A = Intersect(r1, r2)
B = Intersect(r1, r3)
C = Intersect(r2, r3)
regsol(x, y) = a(x, y) ∧ b(x, y) ∧ c(x, y)