add union Chap07 p118 L3
add diff (xxx) Chap07 p118 L4
add intersectall Chap07 p119 L2
add a-pair Chap07 p119 L7
add first, second, build Chap07 p120 L6 (left)
modify first, second, build Chap07 p120 L6 (right)
add third Chap07 p121 L1
add fun? Chap07 p122 L1
add revrel Chap07 p122 L5
modify revrel Chap07 p122 L6 (left)
modify revrel Chap07 p122 L6 (right)
modify revrel Chap07 p123 L1
add fullfun?, seconds Chap07 p123 L6
add one-to-one? (= fullfun?) Chap07 p124 L2