Database SUPPLEMENTARY MATERIAL (USERS' MATHBOXES) Mathbox for Richard Penner Exploring Topology via Seifert and Threlfall Equinumerosity of sets of relations and maps fsovcnvfvd  
				
		 
		
			
		 
		Description:   The value of the converse of ( A O B )  , where O  is the
           operator which maps between maps from one base set to subsets of the
           second to maps from the second base set to subsets of the first for
           base sets, evaluated at function F  .  (Contributed by RP , 27-Apr-2021) 
		
			
				
					Ref 
					Expression 
				 
					
						Hypotheses 
						fsovd.fs   ⊢   O  =    a  ∈  V  ,  b  ∈  V  ⟼    f  ∈    𝒫  b    a   ⟼    y  ∈  b  ⟼   x  ∈  a  |   y  ∈   f  ⁡  x                     
					 
					
						fsovd.a    ⊢   φ   →   A  ∈  V         
					 
					
						fsovd.b    ⊢   φ   →   B  ∈  W         
					 
					
						fsovfvd.g   ⊢   G  =  A  O  B      
					 
					
						fsovcnvfvd.f    ⊢   φ   →   F  ∈    𝒫  A    B          
					 
				
					Assertion 
					fsovcnvfvd    ⊢   φ   →     G  -1    ⁡  F   =    y  ∈  A  ⟼   x  ∈  B  |   y  ∈   F  ⁡  x                 
				 
			
		 
		
				Proof 
				
					
						Step 
						Hyp 
						Ref 
						Expression 
					 
						
							1 
								
							 
							fsovd.fs  ⊢   O  =    a  ∈  V  ,  b  ∈  V  ⟼    f  ∈    𝒫  b    a   ⟼    y  ∈  b  ⟼   x  ∈  a  |   y  ∈   f  ⁡  x                     
						
							2 
								
							 
							fsovd.a   ⊢   φ   →   A  ∈  V         
						
							3 
								
							 
							fsovd.b   ⊢   φ   →   B  ∈  W         
						
							4 
								
							 
							fsovfvd.g  ⊢   G  =  A  O  B      
						
							5 
								
							 
							fsovcnvfvd.f   ⊢   φ   →   F  ∈    𝒫  A    B          
						
							6 
								
							 
							eqid  ⊢   B  O  A =  B  O  A      
						
							7 
								1  2  3  4  6 
							 
							fsovcnvd   ⊢   φ   →    G  -1    =  B  O  A        
						
							8 
								7 
							 
							fveq1d   ⊢   φ   →     G  -1    ⁡  F   =   B  O  A ⁡  F          
						
							9 
								1  3  2  6  5 
							 
							fsovfvd   ⊢   φ   →    B  O  A ⁡  F   =    y  ∈  A  ⟼   x  ∈  B  |   y  ∈   F  ⁡  x                 
						
							10 
								8  9 
							 
							eqtrd   ⊢   φ   →     G  -1    ⁡  F   =    y  ∈  A  ⟼   x  ∈  B  |   y  ∈   F  ⁡  x