Database ZF (ZERMELO-FRAENKEL) SET THEORY ZF Set Theory - start with the Axiom of Extensionality Restricted quantification Restricted universal and existential quantification reximiaOLD  
				
		 
		
			
		 
		Description:   Obsolete version of reximia  as of 31-Oct-2024.  (Contributed by NM , 10-Feb-1997)   (Proof modification is discouraged.) 
       (New usage is discouraged.) 
		
			
				
					Ref 
					Expression 
				 
					
						Hypothesis 
						reximiaOLD.1    ⊢   x  ∈  A    →    φ   →   ψ         
					 
				
					Assertion 
					reximiaOLD    ⊢   ∃  x  ∈  A   φ     →   ∃  x  ∈  A   ψ          
				 
			
		 
		
				Proof 
				
					
						Step 
						Hyp 
						Ref 
						Expression 
					 
						
							1 
								
							 
							reximiaOLD.1   ⊢   x  ∈  A    →    φ   →   ψ         
						
							2 
								
							 
							rexim   ⊢   ∀  x  ∈  A    φ   →   ψ      →    ∃  x  ∈  A   φ     →   ∃  x  ∈  A   ψ           
						
							3 
								2  1 
							 
							mprg   ⊢   ∃  x  ∈  A   φ     →   ∃  x  ∈  A   ψ