225) Stephen Kleene notes that any of the six inequality restrictions on the range of the variable y is permitted, i.e. "y < z", "y ≤ z", "w < y < z", "w < y ≤ z", "w ≤ y < z", "w ≤ y ≤ z".
(p.225) Kleene 提示说对变量 y 的值域的 6 个不等式限制中任何一个都是允许的，它们是 y < z, y ≤ z, w < y < z, w < y ≤ z, w ≤ y < z, w ≤ y ≤ z。