9 BINARY RELATIONS - tmarris.com

79.7 RANGE RESTRICTIONLook again at this binary relation:{ 1 å a, 2 å b, 3 å c }Its range is { a, b, c }.If we restrict the binary relation so that its range is { b } we get{ 2 å b }We write{ 1 å a, 2 å b, 3 å c } t { b } = { 2 å b }where t means range restriction. t is known as the range restriction operator.The range restriction operator defines a subset of a given binary relation. For example:{ 1 å a, 2 å b, 3 å c } t { d } = { }{ 1 å a, 2 å b, 3 å c } t { a, c } = { 1 å a, 3 å c }EXERCISE 9.51 Evaluatea { A, C }r { A å carrots, B1 å pasta, C å potatoes, C å tomatoes, D å milk }b { red å 1, brown å 2, green å 3, yellow å 4, blue å 5, pink å 6, black å 7 } t 3..5c { king } r { pawn å 1, rook å 5, knight å 3, bishop å 3, queen å 9 }d { pawn å 1, rook å 5, knight å 3, bishop å 3, queen å 9 }t { n : Z | n > 3 }