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1. The following “proof by induction” attemps to prove that all horses in univer

ID: 3796132 • Letter: 1

Question

1.       The following “proof by induction” attemps to prove that all horses in universe have the same color. That is, for every n 1, any set of n horses in universe have the same color. Obviously, there is something wrong with this proof. State clearly which step is wrong and why.

(a)    For n = 1, the set contains a single horse, which has the same color by itself, so the base is obviously correct

(b)    For the hypothesis, suppose the claim is correct for some n 1.

(c)    Then, we will prove the claim is also correct for n+1. Consider any set of n+1 horses. Let us number them as 1,2,···,n +1.

i.                     By the hypothesis, horses {1,2,···,n} have the same color.

ii.                   By the hypothesis, horses {2,3,···,n+1} have the same color.

iii.                 These two sets have in common horses {2,3,···,n}.

iv.                 Therefore, by transitivity, these n +1 horses all have the same color

Explanation / Answer

2nd step is wrong.

In 2nd step, by the hypothesis, number of horses should be n+1 but only n horses are taken into the equation (2,3,....n+1)