Database SUPPLEMENTARY MATERIAL (USERS' MATHBOXES) Mathbox for Steven Nguyen Structures pwselbasr  
				
		 
		
			
		 
		Description:   The reverse direction of pwselbasb  : a function between the index and
       base set of a structure is an element of the structure power.
       (Contributed by SN , 29-Jul-2024) 
		
			
				
					Ref 
					Expression 
				 
					
						Hypotheses 
						pwselbasr.y   ⊢   Y  =  R  ↑  𝑠 I      
					 
					
						pwselbasr.b   ⊢   B  =  Base  R      
					 
					
						pwselbasr.v   ⊢   V  =  Base  Y      
					 
					
						pwselbasr.r    ⊢   φ   →   R  ∈  W         
					 
					
						pwselbasr.i    ⊢   φ   →   I  ∈  Z         
					 
					
						pwselbasr.x    ⊢   φ   →   X  :  I  ⟶  B         
					 
				
					Assertion 
					pwselbasr    ⊢   φ   →   X  ∈  V         
				 
			
		 
		
				Proof 
				
					
						Step 
						Hyp 
						Ref 
						Expression 
					 
						
							1 
								
							 
							pwselbasr.y  ⊢   Y  =  R  ↑  𝑠 I      
						
							2 
								
							 
							pwselbasr.b  ⊢   B  =  Base  R      
						
							3 
								
							 
							pwselbasr.v  ⊢   V  =  Base  Y      
						
							4 
								
							 
							pwselbasr.r   ⊢   φ   →   R  ∈  W         
						
							5 
								
							 
							pwselbasr.i   ⊢   φ   →   I  ∈  Z         
						
							6 
								
							 
							pwselbasr.x   ⊢   φ   →   X  :  I  ⟶  B         
						
							7 
								1  2  3 
							 
							pwselbasb   ⊢    R  ∈  W    ∧   I  ∈  Z     →    X  ∈  V    ↔   X  :  I  ⟶  B          
						
							8 
								4  5  7 
							 
							syl2anc   ⊢   φ   →    X  ∈  V    ↔   X  :  I  ⟶  B          
						
							9 
								6  8 
							 
							mpbird   ⊢   φ   →   X  ∈  V