10 lines
		
	
	
	
		
			360 B
		
	
	
	
		
			Markdown
		
	
	
	
	
	
			
		
		
	
	
			10 lines
		
	
	
	
		
			360 B
		
	
	
	
		
			Markdown
		
	
	
	
	
	
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tags:
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  - Logic
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  - propositional-logic
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  - derivation-rules
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The biconditional means if $P$ is the case, $Q$ is the case and if $Q$ is the case, $P$ must be the case. Thus to introduce this operator we must demonstrate both that $Q$ follows from $P$ and that $P$ follows from $Q$. We do this via two sub-proofs. 
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