Problem Solution

Weekly Challenge 15: Indexing Problems

Constructing a really clear argument to this problem can be difficult!

Put simply:

Suppose that exactly one of the following statements is true:

A: Ultra Ref does refer to itself in its index
B: Ultra-Ref does not refer to itself in its index

Look at each in turn:

IF (Ultra-Ref does refer to itself in its index) THEN (Ultra-Ref does not refer to itself in its index)

IF (Ultra-Ref does not refer to itself in its index) THEN (Ultra-Ref does refer to itself in its index)

In both cases, our supposition is contradicted and Ultra-Ref is therefore a logical impossibility.