Set Theoryhard
0:00.0

Let UU be a set of 2102^{10} elements. How many distinct subsets AUA \subseteq U satisfy the condition A{x1,x2,x3,x4}=1|A \cap \{x_1, x_2, x_3, x_4\}| = 1, where x1,x2,x3,x4x_1, x_2, x_3, x_4 are distinct elements of UU?