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# Y is x2 z is roundx2 y z define isoddx y

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Unformatted text preview: tests N to see if it’s an even number Even Numbers Method 2 •  Use the natural number definition and permit only the even ones •  Modify: nn(1).! nn(N) :- nn(M), N is M+1.! •  into even(N) :- nn(N), is_even(N).! •  •  Suppose –  even numbers are natural numbers that are divisible by 2 Let’s use Prolog’s built-in arithmetic evaluation predicate is/2! –  ?- Y is 3/2.! •  –  Y=1.5! –  ?- Y is 4/2.! •  produces an integer –  Y=2! –  ?- Y is round(3/2).! •  where is_even(N) tests N to see if it’s an even number produces a floating point number –  rounds up to the nearest integer Y=2 ! Even Numbers •  •  Definition so far Suppose even(N) :- nn(N), is_even(N).! where is_even(N) tests N to see if it’s an even number Simple Idea: –  to test whether a number X is even 1.  divide it by 2, call this number Y 2.  divide it by 2 and round it, call this number Z 3.  X is even if Y=Z. –  even numbers are natural numbers tha...
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