Database SUPPLEMENTARY MATERIAL (USERS' MATHBOXES) Mathbox for Richard Penner Exploring Topology via Seifert and Threlfall Equinumerosity of sets of relations and maps rfovf1od  
				
		 
		
			
		 
		Description:   The value of the operator, ( A O B )  , which maps between
           relations and functions for relations between base sets, A  and
           B  , is a bijection.  (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 
					rfovf1od ⊢   ( 𝜑   →  𝐹  : 𝒫  ( 𝐴   ×  𝐵  ) –1-1 -onto → ( 𝒫  𝐵   ↑m   𝐴  ) )  
			
		 
		
				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   ↑m   𝐴  )  ∧  ◡ 𝐹   =  ( 𝑓   ∈  ( 𝒫  𝐵   ↑m   𝐴  )  ↦  { 〈 𝑥  ,  𝑦  〉  ∣  ( 𝑥   ∈  𝐴   ∧  𝑦   ∈  ( 𝑓  ‘ 𝑥  ) ) } ) ) )  
						
							6 
								5 
							 
							simpld ⊢  ( 𝜑   →  𝐹  : 𝒫  ( 𝐴   ×  𝐵  ) –1-1 -onto → ( 𝒫  𝐵   ↑m   𝐴  ) )