21. Hence the ordered pair can be taken as a primitive notion, whose associated axiom is the characteristic property. 22. The Digram Round contains a tile representing an ordered pair of letters, which is regarded as a single unit. 23. Back-substituting the second ordered pair gives us x + y = 55, xy = 16, which gives no solutions. 24. Another way to rigorously deal with ordered pairs is to define them formally in the context of set theory. 25. The locks-and-keys approach represents pointers as ordered pairs ( key, address ) where the key is an integer value. 26. Then one way of representing the truth condition of " Nixon is alive " is as the ordered pair . 27. Where " A " is a 2? orthogonal matrix and is an arbitrary ordered pair of numbers; that is, 28. For example, the ordered pair ( 0, 1 ), in the usual construction of the complex numbers with two-dimensional vectors. 29. For an extensive discussion of the ordered pair in the context of Quinian set theories, see Holmes ( 1998 ). 30. For additional clarification, the ordered pair may be denoted by the variant notation, but this notation also has other uses.
