| Step | Hyp | Ref | Expression | 
						
							| 1 |  | ax-1ne0 |  |-  1 =/= 0 | 
						
							| 2 | 1 | a1i |  |-  ( 1 e. O -> 1 =/= 0 ) | 
						
							| 3 |  | snelpwi |  |-  ( 1 e. O -> { 1 } e. ~P O ) | 
						
							| 4 |  | fvres |  |-  ( { 1 } e. ~P O -> ( ( # |` ~P O ) ` { 1 } ) = ( # ` { 1 } ) ) | 
						
							| 5 | 3 4 | syl |  |-  ( 1 e. O -> ( ( # |` ~P O ) ` { 1 } ) = ( # ` { 1 } ) ) | 
						
							| 6 |  | 1re |  |-  1 e. RR | 
						
							| 7 |  | hashsng |  |-  ( 1 e. RR -> ( # ` { 1 } ) = 1 ) | 
						
							| 8 | 6 7 | ax-mp |  |-  ( # ` { 1 } ) = 1 | 
						
							| 9 | 5 8 | eqtrdi |  |-  ( 1 e. O -> ( ( # |` ~P O ) ` { 1 } ) = 1 ) | 
						
							| 10 |  | snssi |  |-  ( 1 e. RR -> { 1 } C_ RR ) | 
						
							| 11 |  | ovolsn |  |-  ( 1 e. RR -> ( vol* ` { 1 } ) = 0 ) | 
						
							| 12 |  | nulmbl |  |-  ( ( { 1 } C_ RR /\ ( vol* ` { 1 } ) = 0 ) -> { 1 } e. dom vol ) | 
						
							| 13 | 10 11 12 | syl2anc |  |-  ( 1 e. RR -> { 1 } e. dom vol ) | 
						
							| 14 |  | mblvol |  |-  ( { 1 } e. dom vol -> ( vol ` { 1 } ) = ( vol* ` { 1 } ) ) | 
						
							| 15 | 6 11 | ax-mp |  |-  ( vol* ` { 1 } ) = 0 | 
						
							| 16 | 14 15 | eqtrdi |  |-  ( { 1 } e. dom vol -> ( vol ` { 1 } ) = 0 ) | 
						
							| 17 | 6 13 16 | mp2b |  |-  ( vol ` { 1 } ) = 0 | 
						
							| 18 | 17 | a1i |  |-  ( 1 e. O -> ( vol ` { 1 } ) = 0 ) | 
						
							| 19 | 2 9 18 | 3netr4d |  |-  ( 1 e. O -> ( ( # |` ~P O ) ` { 1 } ) =/= ( vol ` { 1 } ) ) | 
						
							| 20 |  | fveq1 |  |-  ( ( # |` ~P O ) = vol -> ( ( # |` ~P O ) ` { 1 } ) = ( vol ` { 1 } ) ) | 
						
							| 21 | 20 | necon3i |  |-  ( ( ( # |` ~P O ) ` { 1 } ) =/= ( vol ` { 1 } ) -> ( # |` ~P O ) =/= vol ) | 
						
							| 22 | 19 21 | syl |  |-  ( 1 e. O -> ( # |` ~P O ) =/= vol ) | 
						
							| 23 | 6 13 | ax-mp |  |-  { 1 } e. dom vol | 
						
							| 24 | 23 | biantrur |  |-  ( -. { 1 } e. dom ( # |` ~P O ) <-> ( { 1 } e. dom vol /\ -. { 1 } e. dom ( # |` ~P O ) ) ) | 
						
							| 25 |  | snex |  |-  { 1 } e. _V | 
						
							| 26 | 25 | elpw |  |-  ( { 1 } e. ~P O <-> { 1 } C_ O ) | 
						
							| 27 |  | dmhashres |  |-  dom ( # |` ~P O ) = ~P O | 
						
							| 28 | 27 | eleq2i |  |-  ( { 1 } e. dom ( # |` ~P O ) <-> { 1 } e. ~P O ) | 
						
							| 29 |  | 1ex |  |-  1 e. _V | 
						
							| 30 | 29 | snss |  |-  ( 1 e. O <-> { 1 } C_ O ) | 
						
							| 31 | 26 28 30 | 3bitr4i |  |-  ( { 1 } e. dom ( # |` ~P O ) <-> 1 e. O ) | 
						
							| 32 | 31 | notbii |  |-  ( -. { 1 } e. dom ( # |` ~P O ) <-> -. 1 e. O ) | 
						
							| 33 | 24 32 | bitr3i |  |-  ( ( { 1 } e. dom vol /\ -. { 1 } e. dom ( # |` ~P O ) ) <-> -. 1 e. O ) | 
						
							| 34 |  | nelne1 |  |-  ( ( { 1 } e. dom vol /\ -. { 1 } e. dom ( # |` ~P O ) ) -> dom vol =/= dom ( # |` ~P O ) ) | 
						
							| 35 | 33 34 | sylbir |  |-  ( -. 1 e. O -> dom vol =/= dom ( # |` ~P O ) ) | 
						
							| 36 | 35 | necomd |  |-  ( -. 1 e. O -> dom ( # |` ~P O ) =/= dom vol ) | 
						
							| 37 |  | dmeq |  |-  ( ( # |` ~P O ) = vol -> dom ( # |` ~P O ) = dom vol ) | 
						
							| 38 | 37 | necon3i |  |-  ( dom ( # |` ~P O ) =/= dom vol -> ( # |` ~P O ) =/= vol ) | 
						
							| 39 | 36 38 | syl |  |-  ( -. 1 e. O -> ( # |` ~P O ) =/= vol ) | 
						
							| 40 | 22 39 | pm2.61i |  |-  ( # |` ~P O ) =/= vol |