Theorem bj-ax12v3 36687

Description: A weak version of ax-12 2176 which is stronger than ax12v 2177. Note that if one assumes reflexivity of equality ⊢ 𝑥 = 𝑥 (equid 2010), then bj-ax12v3 36687 implies ax-5 1909 over modal logic K (substitute 𝑥 for 𝑦). See also bj-ax12v3ALT 36688. (Contributed by BJ, 6-Jul-2021.) (Proof modification is discouraged.)

Assertion

Ref	Expression
bj-ax12v3	⊢ (𝑥 = 𝑦 → (𝜑 → ∀𝑥(𝑥 = 𝑦 → 𝜑)))

Distinct variable group:   𝜑,𝑦

Allowed substitution hint:   𝜑(𝑥)

Proof of Theorem bj-ax12v3

Step	Hyp	Ref	Expression
1		ax-5 1909	. 2 ⊢ (𝜑 → ∀𝑦𝜑)
2		ax12 2427	. 2 ⊢ (𝑥 = 𝑦 → (∀𝑦𝜑 → ∀𝑥(𝑥 = 𝑦 → 𝜑)))
3	1, 2	syl5 34	1 ⊢ (𝑥 = 𝑦 → (𝜑 → ∀𝑥(𝑥 = 𝑦 → 𝜑)))

Syntax hints:   → wi 4  ∀wal 1537

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1794  ax-4 1808  ax-5 1909  ax-6 1966  ax-7 2006  ax-10 2140  ax-12 2176  ax-13 2376

This theorem depends on definitions:  df-bi 207  df-an 396  df-ex 1779  df-nf 1783

This theorem is referenced by: (None)