fv.eqext

Theorem.

Arguments:

x (sv), phi (pr),

Assertions:

(forallx(phitoforallxphi)to(existsxphitophi))

Proof:

Hyp Ref Line Expr
fv-negt1(forallx(phitoforallxphi)to(lnotphitoforallxlnotphi))
1con<2(forallx(phitoforallxphi)to(lnotforallxlnotphitophi))
df-ex3(existsxphileftrightarrowlnotforallxlnotphi)
2, 3brpi324(forallx(phitoforallxphi)to(existsxphitophi))