Database ZF (ZERMELO-FRAENKEL) SET THEORY ZF Set Theory - start with the Axiom of Extensionality Unordered and ordered pairs raltp  
				
		 
		
			
		 
		Description:   Convert a universal quantification over an unordered triple to a
       conjunction.  (Contributed by NM , 13-Sep-2011)   (Revised by Mario
       Carneiro , 23-Apr-2015) 
		
			
				
					Ref 
					Expression 
				 
					
						Hypotheses 
						raltp.1   ⊢   A  ∈  V       
					 
					
						raltp.2   ⊢   B  ∈  V       
					 
					
						raltp.3   ⊢   C  ∈  V       
					 
					
						raltp.4    ⊢   x  =  A    →    φ   ↔   ψ         
					 
					
						raltp.5    ⊢   x  =  B    →    φ   ↔   χ         
					 
					
						raltp.6    ⊢   x  =  C    →    φ   ↔   θ         
					 
				
					Assertion 
					raltp    ⊢   ∀  x  ∈   A  B  C     φ     ↔    ψ   ∧   χ   ∧   θ         
				 
			
		 
		
				Proof 
				
					
						Step 
						Hyp 
						Ref 
						Expression 
					 
						
							1 
								
							 
							raltp.1  ⊢   A  ∈  V       
						
							2 
								
							 
							raltp.2  ⊢   B  ∈  V       
						
							3 
								
							 
							raltp.3  ⊢   C  ∈  V       
						
							4 
								
							 
							raltp.4   ⊢   x  =  A    →    φ   ↔   ψ         
						
							5 
								
							 
							raltp.5   ⊢   x  =  B    →    φ   ↔   χ         
						
							6 
								
							 
							raltp.6   ⊢   x  =  C    →    φ   ↔   θ         
						
							7 
								4  5  6 
							 
							raltpg   ⊢    A  ∈  V    ∧   B  ∈  V    ∧   C  ∈  V     →    ∀  x  ∈   A  B  C     φ     ↔    ψ   ∧   χ   ∧   θ          
						
							8 
								1  2  3  7 
							 
							mp3an   ⊢   ∀  x  ∈   A  B  C     φ     ↔    ψ   ∧   χ   ∧   θ