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## Homework Statement

Let X be a finite set and let x be an object which is not an element of X. Then X U {x} is finite and #(X U {x}) = #(X) + 1

## The Attempt at a Solution

Let X be a finite set such that X has cardinality n, denoted by #X.

Suppose that ## x \notin X##, then the set X U {x} has cardinality n + 1, that is #X +1, as required.

If i must be honest, i don't think i have proven anything :(

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