Theorem nornotOLD

Description: Obsolete version of nornot as of 8-Dec-2023. (Contributed by Remi, 25-Oct-2023) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	nornotOLD	$$⊢\neg \phi \leftrightarrow \left(\phi ⊽\phi \right)$$

Proof

Step	Hyp	Ref	Expression
1		pm4.56	$$⊢\left(\neg \phi \wedge \neg \phi \right)\leftrightarrow \neg \left(\phi \vee \phi \right)$$
2		pm4.24	$$⊢\neg \phi \leftrightarrow \left(\neg \phi \wedge \neg \phi \right)$$
3		df-nor	$$⊢\left(\phi ⊽\phi \right)\leftrightarrow \neg \left(\phi \vee \phi \right)$$
4	1 2 3	3bitr4i	$$⊢\neg \phi \leftrightarrow \left(\phi ⊽\phi \right)$$