Theorem frege52aid 38993

Description: The case when the content of 𝜑 is identical with the content of 𝜓 and in which 𝜑 is affirmed and 𝜓 is denied does not take place. Identical to biimp 207. Part of Axiom 52 of [Frege1879] p. 50. (Contributed by RP, 24-Dec-2019.) (Proof modification is discouraged.)

Assertion

Ref	Expression
frege52aid	⊢ ((𝜑 ↔ 𝜓) → (𝜑 → 𝜓))

Proof of Theorem frege52aid

Step	Hyp	Ref	Expression
1		ax-frege52a 38992	. 2 ⊢ ((𝜑 ↔ 𝜓) → (if-(𝜑, ⊤, ⊥) → if-(𝜓, ⊤, ⊥)))
2		ifpid2 38658	. 2 ⊢ (𝜑 ↔ if-(𝜑, ⊤, ⊥))
3		ifpid2 38658	. 2 ⊢ (𝜓 ↔ if-(𝜓, ⊤, ⊥))
4	1, 2, 3	3imtr4g 288	1 ⊢ ((𝜑 ↔ 𝜓) → (𝜑 → 𝜓))

Syntax hints:   → wi 4   ↔ wb 198  if-wif 1091  ⊤wtru 1659  ⊥wfal 1671

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-frege52a 38992

This theorem depends on definitions:  df-bi 199  df-an 387  df-or 881  df-ifp 1092  df-tru 1662  df-fal 1672

This theorem is referenced by:  frege53aid  38994  frege57aid  39007  frege75  39073  frege89  39087  frege105  39103