Metamath Proof Explorer

Theorem 19.9d

Description: A deduction version of one direction of 19.9 . (Contributed by NM, 14-May-1993) (Revised by Mario Carneiro, 24-Sep-2016) Revised to shorten other proofs. (Revised by Wolf Lammen, 14-Jul-2020) df-nf changed. (Revised by Wolf Lammen, 11-Sep-2021) (Proof shortened by Wolf Lammen, 8-Jul-2022)

Ref Expression
Hypothesis 19.9d.1 ψ x φ
Assertion 19.9d ψ x φ φ


Step Hyp Ref Expression
1 19.9d.1 ψ x φ
2 1 nfrd ψ x φ x φ
3 sp x φ φ
4 2 3 syl6 ψ x φ φ