Barber Paradox/Analysis 1

Paradox
There exists a community, one of whose members is a barber.

This barber operated under an unusual rule: his task was to shave every man in the community who did not shave himself, and only those men.

Who shaves the barber?

If he does not shave himself, then he must shave himself.

But if he shaves himself, he must not shave himself.

Analysis
This is an application of Russell's Paradox.

Let $\mathbb U$ be the set of all members of the community, and thus treated as the universe.

Let $S: \mathbb U \to \left\{{T, F}\right\}$ be the propositional function:
 * $\forall x \in \mathbb U: S \left({x}\right) \iff x \text { is shaved by $x$}$

Let $b \in \mathbb U$ be the barber.

Let $B: \mathbb U \to \left\{{T, F}\right\}$ be the propositional function:
 * $\forall x \in \mathbb U: B \left({x}\right) \iff x \text { is shaved by $b$}$

The initial premises can be coded:
 * $(1): \quad \forall x \in \mathbb U: \left({\neg S \left({x}\right)}\right) \iff B \left({x}\right)$
 * $(2): \quad B \left({b}\right) \iff S \left({b}\right)$

Hence:
 * $S \left({b}\right) \iff B \left({b}\right) \iff \left({\neg S \left({b}\right)}\right)$

and so from Biconditional is Transitive:
 * $B \left({b}\right) \iff \left({\neg S \left({b}\right)}\right)$

So from either case there derives a contradiction.

Thus the initial premises are contradictory and cannot both hold.