Theorem wl-had1

Description: If the first input is true, then the adder sum is equivalent to the biconditionality of the other two inputs. (Contributed by Mario Carneiro, 4-Sep-2016) Alternative definition. (Revised by Wolf Lammen, 24-Apr-2024)

	Ref	Expression
Assertion	wl-had1	$$⊢\phi \to \left(hadd\left(\phi ,\psi ,\chi \right)\leftrightarrow \left(\psi \leftrightarrow \chi \right)\right)$$

Proof

Step	Hyp	Ref	Expression
1		wl-df-had	$$⊢hadd\left(\phi ,\psi ,\chi \right)\leftrightarrow if-\left(\phi ,\left(\psi \leftrightarrow \chi \right),\left(\psi ⊻\chi \right)\right)$$
2		ifptru	$$⊢\phi \to \left(if-\left(\phi ,\left(\psi \leftrightarrow \chi \right),\left(\psi ⊻\chi \right)\right)\leftrightarrow \left(\psi \leftrightarrow \chi \right)\right)$$
3	1 2	syl5bb	$$⊢\phi \to \left(hadd\left(\phi ,\psi ,\chi \right)\leftrightarrow \left(\psi \leftrightarrow \chi \right)\right)$$