Задача
The elements of the sets A, P and Q are natural numbers, and P = { 2, 4, 6, 8, 10, 12, 14, 16, 18, 20} and Q = { 5, 10, 15, 20, 25, 30 , 35, 40, 45, 50}. It is known that the expression
((x ∈ A) → (x ∈ P)) /\ ((< em>x ∈ Q) → ¬(x ∈ A))
true (i.e. takes the value 1) for any value of the variable
x.
Determine the largest possible number of elements of the set A