a(x, y) = 2 * x + y > -1
b(x, y) = 2 * y ≤ -x + 4
c(x, y) = x < y + 1
d: a(x, y) ∧ b(x, y) ∧ c(x, y)
e: c(x, y) ∨ b(x, y)