Metamath Proof Explorer


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 𝑥

Proof

Step Hyp Ref Expression
1 tru
2 1 exgen 𝑥