Binary Relations (reflexivity)

A binary relation on S is reflexive provided that for every element in S, the pair of that element with itself is a pair in S.

S = { a, b, c }

R4 = { (a, a), (a, b), (b, b), (b, c), (c, c) }

is reflexive.

R5 = { (a, a), (a, b), (b, b) } is not reflexive, because c ? S but (c, c) ?R5.

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