| Step | Hyp | Ref | Expression | 
						
							| 1 |  | id |  |-  ( m = M -> m = M ) | 
						
							| 2 |  | oveq1 |  |-  ( n = N -> ( n - 1 ) = ( N - 1 ) ) | 
						
							| 3 | 1 2 | oveqan12d |  |-  ( ( m = M /\ n = N ) -> ( m ... ( n - 1 ) ) = ( M ... ( N - 1 ) ) ) | 
						
							| 4 |  | df-fzo |  |-  ..^ = ( m e. ZZ , n e. ZZ |-> ( m ... ( n - 1 ) ) ) | 
						
							| 5 |  | ovex |  |-  ( M ... ( N - 1 ) ) e. _V | 
						
							| 6 | 3 4 5 | ovmpoa |  |-  ( ( M e. ZZ /\ N e. ZZ ) -> ( M ..^ N ) = ( M ... ( N - 1 ) ) ) | 
						
							| 7 |  | simpl |  |-  ( ( M e. ZZ /\ N e. ZZ ) -> M e. ZZ ) | 
						
							| 8 |  | fzof |  |-  ..^ : ( ZZ X. ZZ ) --> ~P ZZ | 
						
							| 9 | 8 | fdmi |  |-  dom ..^ = ( ZZ X. ZZ ) | 
						
							| 10 | 9 | ndmov |  |-  ( -. ( M e. ZZ /\ N e. ZZ ) -> ( M ..^ N ) = (/) ) | 
						
							| 11 | 7 10 | nsyl5 |  |-  ( -. M e. ZZ -> ( M ..^ N ) = (/) ) | 
						
							| 12 |  | simpl |  |-  ( ( M e. ZZ /\ ( N - 1 ) e. ZZ ) -> M e. ZZ ) | 
						
							| 13 |  | fzf |  |-  ... : ( ZZ X. ZZ ) --> ~P ZZ | 
						
							| 14 | 13 | fdmi |  |-  dom ... = ( ZZ X. ZZ ) | 
						
							| 15 | 14 | ndmov |  |-  ( -. ( M e. ZZ /\ ( N - 1 ) e. ZZ ) -> ( M ... ( N - 1 ) ) = (/) ) | 
						
							| 16 | 12 15 | nsyl5 |  |-  ( -. M e. ZZ -> ( M ... ( N - 1 ) ) = (/) ) | 
						
							| 17 | 11 16 | eqtr4d |  |-  ( -. M e. ZZ -> ( M ..^ N ) = ( M ... ( N - 1 ) ) ) | 
						
							| 18 | 17 | adantr |  |-  ( ( -. M e. ZZ /\ N e. ZZ ) -> ( M ..^ N ) = ( M ... ( N - 1 ) ) ) | 
						
							| 19 | 6 18 | pm2.61ian |  |-  ( N e. ZZ -> ( M ..^ N ) = ( M ... ( N - 1 ) ) ) |