Chapter 2 Relations Definition 2.1: An order pair (a, b) is a listing of the objects a and b in a prescribed order, with a appearing first and b appearing second. Two order pairs(a, b)and (c, d) are equal if only if a=c and b=d {a,b}={b,a}, order pairs: (a, b)=(b, a)unless a=b aaChapter 2 Relations Definition 2.1: An order pair (a,b) is a listing of the objects a and b in a prescribed order, with a appearing first and b appearing second. Two order pairs (a,b) and (c, d) are equal if only if a=c and b=d. {a,b}={b,a}， order pairs: (a,b)(b,a) unless a=b. (a,a)