Database SUPPLEMENTARY MATERIAL (USERS' MATHBOXES) Mathbox for Richard Penner Exploring Topology via Seifert and Threlfall Equinumerosity of sets of relations and maps rfovcnvd  
				
		 
		
			
		 
		Description:   Value of the converse of the operator, ( A O B )  , which maps
           between relations and functions for relations between base sets,
           A  and B  .  (Contributed by RP , 27-Apr-2021) 
		
			
				
					Ref 
					Expression 
				 
					
						Hypotheses 
						rfovd.rf   ⊢   O  =    a  ∈  V  ,  b  ∈  V  ⟼    r  ∈   𝒫   a  ×  b     ⟼    x  ∈  a  ⟼   y  ∈  b  |  x  r  y                 
					 
					
						rfovd.a    ⊢   φ   →   A  ∈  V         
					 
					
						rfovd.b    ⊢   φ   →   B  ∈  W         
					 
					
						rfovcnvf1od.f   ⊢   F  =  A  O  B      
					 
				
					Assertion 
					rfovcnvd    ⊢   φ   →    F  -1    =    f  ∈    𝒫  B    A   ⟼   x  y |    x  ∈  A    ∧   y  ∈   f  ⁡  x                  
				 
			
		 
		
				Proof 
				
					
						Step 
						Hyp 
						Ref 
						Expression 
					 
						
							1 
								
							 
							rfovd.rf  ⊢   O  =    a  ∈  V  ,  b  ∈  V  ⟼    r  ∈   𝒫   a  ×  b     ⟼    x  ∈  a  ⟼   y  ∈  b  |  x  r  y                 
						
							2 
								
							 
							rfovd.a   ⊢   φ   →   A  ∈  V         
						
							3 
								
							 
							rfovd.b   ⊢   φ   →   B  ∈  W         
						
							4 
								
							 
							rfovcnvf1od.f  ⊢   F  =  A  O  B      
						
							5 
								1  2  3  4 
							 
							rfovcnvf1od   ⊢   φ   →    F  :   𝒫   A  ×  B     ⟶  1-1 onto   𝒫  B    A      ∧    F  -1    =    f  ∈    𝒫  B    A   ⟼   x  y |    x  ∈  A    ∧   y  ∈   f  ⁡  x                   
						
							6 
								5 
							 
							simprd   ⊢   φ   →    F  -1    =    f  ∈    𝒫  B    A   ⟼   x  y |    x  ∈  A    ∧   y  ∈   f  ⁡  x