Theorem wl-luk-id

Description: Principle of identity. Theorem *2.08 of WhiteheadRussell p. 101. Copy of id with a different proof. (Contributed by Wolf Lammen, 17-Dec-2018) (New usage is discouraged.) (Proof modification is discouraged.)

	Ref	Expression
Assertion	wl-luk-id	$$⊢\phi \to \phi$$

Proof

Step	Hyp	Ref	Expression
1		ax-luk3	$$⊢\phi \to \left(\neg \phi \to \phi \right)$$
2		ax-luk2	$$⊢\left(\neg \phi \to \phi \right)\to \phi$$
3	1 2	wl-luk-syl	$$⊢\phi \to \phi$$