MathCastle
Proof Writing & Problem SolvingSuperchallenge

Proof Writing & Problem Solving · Superchallenge problem

A relation RR on {1,2,3}\{1, 2, 3\} is any set of ordered pairs (x,y)(x, y) with x,y∈{1,2,3}x, y \in \{1, 2, 3\}; there are 29=5122^9 = 512 of them. For how many relations RR is the statement "for every xx there is a yy with (x,y)∈R(x, y) \in R" true, but the statement "there is a yy such that for every xx, (x,y)∈R(x, y) \in R" false?

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