It is known that the definition field of function y = LG (4-x) is a, and set B = {x | x ＜ a}. If P: "x ∈ a" is a sufficient and unnecessary condition of Q: "x ∈ B", then the real number a Why is it greater than 4 instead of less than 4? Isn't the sufficient and unnecessary condition that a can deduce B, but B can't deduce a

It is known that the definition field of function y = LG (4-x) is a, and set B = {x | x ＜ a}. If P: "x ∈ a" is a sufficient and unnecessary condition of Q: "x ∈ B", then the real number a Why is it greater than 4 instead of less than 4? Isn't the sufficient and unnecessary condition that a can deduce B, but B can't deduce a

A is interval (- ∞, 4)
B is interval (- ∞, a)
P is a sufficient and unnecessary condition for Q, that is to say:
If P is true, then q is also true (i.e. x = 4), but q is true, i.e. the value of x > = 4 exists in the interval (- ∞, a), so a > 4
A > 4