| Step | 
						Hyp | 
						Ref | 
						Expression | 
					
						
							| 1 | 
							
								
							 | 
							evenz | 
							⊢ ( 𝑍  ∈   Even   →  𝑍  ∈  ℤ )  | 
						
						
							| 2 | 
							
								1
							 | 
							peano2zd | 
							⊢ ( 𝑍  ∈   Even   →  ( 𝑍  +  1 )  ∈  ℤ )  | 
						
						
							| 3 | 
							
								
							 | 
							iseven | 
							⊢ ( 𝑍  ∈   Even   ↔  ( 𝑍  ∈  ℤ  ∧  ( 𝑍  /  2 )  ∈  ℤ ) )  | 
						
						
							| 4 | 
							
								
							 | 
							zcn | 
							⊢ ( 𝑍  ∈  ℤ  →  𝑍  ∈  ℂ )  | 
						
						
							| 5 | 
							
								
							 | 
							pncan1 | 
							⊢ ( 𝑍  ∈  ℂ  →  ( ( 𝑍  +  1 )  −  1 )  =  𝑍 )  | 
						
						
							| 6 | 
							
								4 5
							 | 
							syl | 
							⊢ ( 𝑍  ∈  ℤ  →  ( ( 𝑍  +  1 )  −  1 )  =  𝑍 )  | 
						
						
							| 7 | 
							
								6
							 | 
							eqcomd | 
							⊢ ( 𝑍  ∈  ℤ  →  𝑍  =  ( ( 𝑍  +  1 )  −  1 ) )  | 
						
						
							| 8 | 
							
								7
							 | 
							oveq1d | 
							⊢ ( 𝑍  ∈  ℤ  →  ( 𝑍  /  2 )  =  ( ( ( 𝑍  +  1 )  −  1 )  /  2 ) )  | 
						
						
							| 9 | 
							
								8
							 | 
							eleq1d | 
							⊢ ( 𝑍  ∈  ℤ  →  ( ( 𝑍  /  2 )  ∈  ℤ  ↔  ( ( ( 𝑍  +  1 )  −  1 )  /  2 )  ∈  ℤ ) )  | 
						
						
							| 10 | 
							
								9
							 | 
							biimpa | 
							⊢ ( ( 𝑍  ∈  ℤ  ∧  ( 𝑍  /  2 )  ∈  ℤ )  →  ( ( ( 𝑍  +  1 )  −  1 )  /  2 )  ∈  ℤ )  | 
						
						
							| 11 | 
							
								3 10
							 | 
							sylbi | 
							⊢ ( 𝑍  ∈   Even   →  ( ( ( 𝑍  +  1 )  −  1 )  /  2 )  ∈  ℤ )  | 
						
						
							| 12 | 
							
								
							 | 
							isodd2 | 
							⊢ ( ( 𝑍  +  1 )  ∈   Odd   ↔  ( ( 𝑍  +  1 )  ∈  ℤ  ∧  ( ( ( 𝑍  +  1 )  −  1 )  /  2 )  ∈  ℤ ) )  | 
						
						
							| 13 | 
							
								2 11 12
							 | 
							sylanbrc | 
							⊢ ( 𝑍  ∈   Even   →  ( 𝑍  +  1 )  ∈   Odd  )  |