CombinatoricsDifficulty 4.5AIMEFind the answerUnited States
Problem: Find the number of pairs of union/intersection operations (□1,□2)∈{∪,∩}2 satisfying the following condition: for any sets S,T, function f:S→T, and subsets X,Y,Z of S, we have equality of sets f(X)□1(f(Y)□2f(Z))=f(X□1(Y□2Z)), where f(X) denotes the image of X : the set {f(x):x∈X}, which is a subset of T. The images f(Y) (of Y ) and f(Z) (of Z ) are similarly defined.
A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.
Solution
Solution: Answer: 1 If and only if □1=□2=∪. See http://math.stackexchange.com/questions/359693/overview-of-1
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