Database ZF (ZERMELO-FRAENKEL) SET THEORY ZF Set Theory - start with the Axiom of Extensionality Functions in maps-to notation mpteq2iaOLD  
				
		 
		
			
		 
		Description:   Obsolete version of mpteq2ia  as of 11-Nov-2024.  (Contributed by Mario
       Carneiro , 16-Dec-2013)   (Proof modification is discouraged.) 
       (New usage is discouraged.) 
		
			
				
					Ref 
					Expression 
				 
					
						Hypothesis 
						mpteq2ia.1    ⊢   x  ∈  A    →   B  =  C         
					 
				
					Assertion 
					mpteq2iaOLD   ⊢     x  ∈  A  ⟼  B     =    x  ∈  A  ⟼  C          
				 
			
		 
		
				Proof 
				
					
						Step 
						Hyp 
						Ref 
						Expression 
					 
						
							1 
								
							 
							mpteq2ia.1   ⊢   x  ∈  A    →   B  =  C         
						
							2 
								
							 
							eqid  ⊢   A  =  A       
						
							3 
								2 
							 
							ax-gen  ⊢   ∀  x   A  =  A         
						
							4 
								1 
							 
							rgen  ⊢   ∀  x  ∈  A   B  =  C         
						
							5 
								
							 
							mpteq12f   ⊢    ∀  x   A  =  A      ∧   ∀  x  ∈  A   B  =  C       →     x  ∈  A  ⟼  B     =    x  ∈  A  ⟼  C            
						
							6 
								3  4  5 
							 
							mp2an  ⊢     x  ∈  A  ⟼  B     =    x  ∈  A  ⟼  C