Metamath Proof Explorer


Theorem axi9

Description: Axiom of existence (intuitionistic logic axiom ax-i9). In classical logic, this is equivalent to ax-6 but in intuitionistic logic it needs to be stated using the existential quantifier. (Contributed by Jim Kingdon, 31-Dec-2017) (New usage is discouraged.)

Ref Expression
Assertion axi9
|- E. x x = y

Proof

Step Hyp Ref Expression
1 ax6e
 |-  E. x x = y