Metamath Proof Explorer
		
		
		
		Description:  The composition of two sets is a set.  (Contributed by SN, 7-Feb-2025)
		
			
				
					 | 
					 | 
					Ref | 
					Expression | 
				
					
						 | 
						Hypotheses | 
						coexd.1 | 
						⊢ ( 𝜑  →  𝐴  ∈  𝑉 )  | 
					
					
						 | 
						 | 
						coexd.2 | 
						⊢ ( 𝜑  →  𝐵  ∈  𝑊 )  | 
					
				
					 | 
					Assertion | 
					coexd | 
					⊢  ( 𝜑  →  ( 𝐴  ∘  𝐵 )  ∈  V )  | 
				
			
		
		
			
				Proof
				
					
						| Step | 
						Hyp | 
						Ref | 
						Expression | 
					
						
							| 1 | 
							
								
							 | 
							coexd.1 | 
							⊢ ( 𝜑  →  𝐴  ∈  𝑉 )  | 
						
						
							| 2 | 
							
								
							 | 
							coexd.2 | 
							⊢ ( 𝜑  →  𝐵  ∈  𝑊 )  | 
						
						
							| 3 | 
							
								
							 | 
							coexg | 
							⊢ ( ( 𝐴  ∈  𝑉  ∧  𝐵  ∈  𝑊 )  →  ( 𝐴  ∘  𝐵 )  ∈  V )  | 
						
						
							| 4 | 
							
								1 2 3
							 | 
							syl2anc | 
							⊢ ( 𝜑  →  ( 𝐴  ∘  𝐵 )  ∈  V )  |