Theorem extru

Description: There exists a variable such that T. holds; that is, there exists a variable. This corresponds under the standard translation to one of the formulations of the modal axiom (D), the other being 19.2 . (Contributed by Anthony Hart, 13-Sep-2011) (Proof shortened by BJ, 12-May-2019)

	Ref	Expression
Assertion	extru	$$⊢\exists x\top$$

Proof

Step	Hyp	Ref	Expression
1		tru	$$⊢\top$$
2	1	exgen	$$⊢\exists x\top$$