Theorem ifpdfor

Description: Define or in terms of conditional logic operator and true. (Contributed by RP, 20-Apr-2020)

	Ref	Expression
Assertion	ifpdfor	$$⊢\left(\phi \vee \psi \right)\leftrightarrow if-\left(\phi ,\top ,\psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		tru	$$⊢\top$$
2	1	olci	$$⊢\left(\neg \phi \vee \top \right)$$
3	2	biantrur	$$⊢\left(\phi \vee \psi \right)\leftrightarrow \left(\left(\neg \phi \vee \top \right)\wedge \left(\phi \vee \psi \right)\right)$$
4		dfifp4	$$⊢if-\left(\phi ,\top ,\psi \right)\leftrightarrow \left(\left(\neg \phi \vee \top \right)\wedge \left(\phi \vee \psi \right)\right)$$
5	3 4	bitr4i	$$⊢\left(\phi \vee \psi \right)\leftrightarrow if-\left(\phi ,\top ,\psi \right)$$