| Step | Hyp | Ref | Expression | 
						
							| 1 |  | neq0 |  |-  ( -. x = (/) <-> E. y y e. x ) | 
						
							| 2 |  | indistop |  |-  { (/) , A } e. Top | 
						
							| 3 |  | indistop |  |-  { (/) , B } e. Top | 
						
							| 4 |  | eltx |  |-  ( ( { (/) , A } e. Top /\ { (/) , B } e. Top ) -> ( x e. ( { (/) , A } tX { (/) , B } ) <-> A. y e. x E. z e. { (/) , A } E. w e. { (/) , B } ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) ) | 
						
							| 5 | 2 3 4 | mp2an |  |-  ( x e. ( { (/) , A } tX { (/) , B } ) <-> A. y e. x E. z e. { (/) , A } E. w e. { (/) , B } ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) | 
						
							| 6 |  | rsp |  |-  ( A. y e. x E. z e. { (/) , A } E. w e. { (/) , B } ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) -> ( y e. x -> E. z e. { (/) , A } E. w e. { (/) , B } ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) ) | 
						
							| 7 | 5 6 | sylbi |  |-  ( x e. ( { (/) , A } tX { (/) , B } ) -> ( y e. x -> E. z e. { (/) , A } E. w e. { (/) , B } ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) ) | 
						
							| 8 |  | elssuni |  |-  ( x e. ( { (/) , A } tX { (/) , B } ) -> x C_ U. ( { (/) , A } tX { (/) , B } ) ) | 
						
							| 9 |  | indisuni |  |-  ( _I ` A ) = U. { (/) , A } | 
						
							| 10 |  | indisuni |  |-  ( _I ` B ) = U. { (/) , B } | 
						
							| 11 | 2 3 9 10 | txunii |  |-  ( ( _I ` A ) X. ( _I ` B ) ) = U. ( { (/) , A } tX { (/) , B } ) | 
						
							| 12 | 8 11 | sseqtrrdi |  |-  ( x e. ( { (/) , A } tX { (/) , B } ) -> x C_ ( ( _I ` A ) X. ( _I ` B ) ) ) | 
						
							| 13 | 12 | ad2antrr |  |-  ( ( ( x e. ( { (/) , A } tX { (/) , B } ) /\ ( z e. { (/) , A } /\ w e. { (/) , B } ) ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> x C_ ( ( _I ` A ) X. ( _I ` B ) ) ) | 
						
							| 14 |  | ne0i |  |-  ( y e. ( z X. w ) -> ( z X. w ) =/= (/) ) | 
						
							| 15 | 14 | ad2antrl |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> ( z X. w ) =/= (/) ) | 
						
							| 16 |  | xpnz |  |-  ( ( z =/= (/) /\ w =/= (/) ) <-> ( z X. w ) =/= (/) ) | 
						
							| 17 | 15 16 | sylibr |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> ( z =/= (/) /\ w =/= (/) ) ) | 
						
							| 18 | 17 | simpld |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> z =/= (/) ) | 
						
							| 19 | 18 | neneqd |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> -. z = (/) ) | 
						
							| 20 |  | simpll |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> z e. { (/) , A } ) | 
						
							| 21 |  | indislem |  |-  { (/) , ( _I ` A ) } = { (/) , A } | 
						
							| 22 | 20 21 | eleqtrrdi |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> z e. { (/) , ( _I ` A ) } ) | 
						
							| 23 |  | elpri |  |-  ( z e. { (/) , ( _I ` A ) } -> ( z = (/) \/ z = ( _I ` A ) ) ) | 
						
							| 24 | 22 23 | syl |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> ( z = (/) \/ z = ( _I ` A ) ) ) | 
						
							| 25 | 24 | ord |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> ( -. z = (/) -> z = ( _I ` A ) ) ) | 
						
							| 26 | 19 25 | mpd |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> z = ( _I ` A ) ) | 
						
							| 27 | 17 | simprd |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> w =/= (/) ) | 
						
							| 28 | 27 | neneqd |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> -. w = (/) ) | 
						
							| 29 |  | simplr |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> w e. { (/) , B } ) | 
						
							| 30 |  | indislem |  |-  { (/) , ( _I ` B ) } = { (/) , B } | 
						
							| 31 | 29 30 | eleqtrrdi |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> w e. { (/) , ( _I ` B ) } ) | 
						
							| 32 |  | elpri |  |-  ( w e. { (/) , ( _I ` B ) } -> ( w = (/) \/ w = ( _I ` B ) ) ) | 
						
							| 33 | 31 32 | syl |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> ( w = (/) \/ w = ( _I ` B ) ) ) | 
						
							| 34 | 33 | ord |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> ( -. w = (/) -> w = ( _I ` B ) ) ) | 
						
							| 35 | 28 34 | mpd |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> w = ( _I ` B ) ) | 
						
							| 36 | 26 35 | xpeq12d |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> ( z X. w ) = ( ( _I ` A ) X. ( _I ` B ) ) ) | 
						
							| 37 |  | simprr |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> ( z X. w ) C_ x ) | 
						
							| 38 | 36 37 | eqsstrrd |  |-  ( ( ( z e. { (/) , A } /\ w e. { (/) , B } ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> ( ( _I ` A ) X. ( _I ` B ) ) C_ x ) | 
						
							| 39 | 38 | adantll |  |-  ( ( ( x e. ( { (/) , A } tX { (/) , B } ) /\ ( z e. { (/) , A } /\ w e. { (/) , B } ) ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> ( ( _I ` A ) X. ( _I ` B ) ) C_ x ) | 
						
							| 40 | 13 39 | eqssd |  |-  ( ( ( x e. ( { (/) , A } tX { (/) , B } ) /\ ( z e. { (/) , A } /\ w e. { (/) , B } ) ) /\ ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) ) -> x = ( ( _I ` A ) X. ( _I ` B ) ) ) | 
						
							| 41 | 40 | ex |  |-  ( ( x e. ( { (/) , A } tX { (/) , B } ) /\ ( z e. { (/) , A } /\ w e. { (/) , B } ) ) -> ( ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) -> x = ( ( _I ` A ) X. ( _I ` B ) ) ) ) | 
						
							| 42 | 41 | rexlimdvva |  |-  ( x e. ( { (/) , A } tX { (/) , B } ) -> ( E. z e. { (/) , A } E. w e. { (/) , B } ( y e. ( z X. w ) /\ ( z X. w ) C_ x ) -> x = ( ( _I ` A ) X. ( _I ` B ) ) ) ) | 
						
							| 43 | 7 42 | syld |  |-  ( x e. ( { (/) , A } tX { (/) , B } ) -> ( y e. x -> x = ( ( _I ` A ) X. ( _I ` B ) ) ) ) | 
						
							| 44 | 43 | exlimdv |  |-  ( x e. ( { (/) , A } tX { (/) , B } ) -> ( E. y y e. x -> x = ( ( _I ` A ) X. ( _I ` B ) ) ) ) | 
						
							| 45 | 1 44 | biimtrid |  |-  ( x e. ( { (/) , A } tX { (/) , B } ) -> ( -. x = (/) -> x = ( ( _I ` A ) X. ( _I ` B ) ) ) ) | 
						
							| 46 | 45 | orrd |  |-  ( x e. ( { (/) , A } tX { (/) , B } ) -> ( x = (/) \/ x = ( ( _I ` A ) X. ( _I ` B ) ) ) ) | 
						
							| 47 |  | vex |  |-  x e. _V | 
						
							| 48 | 47 | elpr |  |-  ( x e. { (/) , ( ( _I ` A ) X. ( _I ` B ) ) } <-> ( x = (/) \/ x = ( ( _I ` A ) X. ( _I ` B ) ) ) ) | 
						
							| 49 | 46 48 | sylibr |  |-  ( x e. ( { (/) , A } tX { (/) , B } ) -> x e. { (/) , ( ( _I ` A ) X. ( _I ` B ) ) } ) | 
						
							| 50 | 49 | ssriv |  |-  ( { (/) , A } tX { (/) , B } ) C_ { (/) , ( ( _I ` A ) X. ( _I ` B ) ) } | 
						
							| 51 | 9 | toptopon |  |-  ( { (/) , A } e. Top <-> { (/) , A } e. ( TopOn ` ( _I ` A ) ) ) | 
						
							| 52 | 2 51 | mpbi |  |-  { (/) , A } e. ( TopOn ` ( _I ` A ) ) | 
						
							| 53 | 10 | toptopon |  |-  ( { (/) , B } e. Top <-> { (/) , B } e. ( TopOn ` ( _I ` B ) ) ) | 
						
							| 54 | 3 53 | mpbi |  |-  { (/) , B } e. ( TopOn ` ( _I ` B ) ) | 
						
							| 55 |  | txtopon |  |-  ( ( { (/) , A } e. ( TopOn ` ( _I ` A ) ) /\ { (/) , B } e. ( TopOn ` ( _I ` B ) ) ) -> ( { (/) , A } tX { (/) , B } ) e. ( TopOn ` ( ( _I ` A ) X. ( _I ` B ) ) ) ) | 
						
							| 56 | 52 54 55 | mp2an |  |-  ( { (/) , A } tX { (/) , B } ) e. ( TopOn ` ( ( _I ` A ) X. ( _I ` B ) ) ) | 
						
							| 57 |  | topgele |  |-  ( ( { (/) , A } tX { (/) , B } ) e. ( TopOn ` ( ( _I ` A ) X. ( _I ` B ) ) ) -> ( { (/) , ( ( _I ` A ) X. ( _I ` B ) ) } C_ ( { (/) , A } tX { (/) , B } ) /\ ( { (/) , A } tX { (/) , B } ) C_ ~P ( ( _I ` A ) X. ( _I ` B ) ) ) ) | 
						
							| 58 | 56 57 | ax-mp |  |-  ( { (/) , ( ( _I ` A ) X. ( _I ` B ) ) } C_ ( { (/) , A } tX { (/) , B } ) /\ ( { (/) , A } tX { (/) , B } ) C_ ~P ( ( _I ` A ) X. ( _I ` B ) ) ) | 
						
							| 59 | 58 | simpli |  |-  { (/) , ( ( _I ` A ) X. ( _I ` B ) ) } C_ ( { (/) , A } tX { (/) , B } ) | 
						
							| 60 | 50 59 | eqssi |  |-  ( { (/) , A } tX { (/) , B } ) = { (/) , ( ( _I ` A ) X. ( _I ` B ) ) } | 
						
							| 61 |  | txindislem |  |-  ( ( _I ` A ) X. ( _I ` B ) ) = ( _I ` ( A X. B ) ) | 
						
							| 62 | 61 | preq2i |  |-  { (/) , ( ( _I ` A ) X. ( _I ` B ) ) } = { (/) , ( _I ` ( A X. B ) ) } | 
						
							| 63 |  | indislem |  |-  { (/) , ( _I ` ( A X. B ) ) } = { (/) , ( A X. B ) } | 
						
							| 64 | 60 62 63 | 3eqtri |  |-  ( { (/) , A } tX { (/) , B } ) = { (/) , ( A X. B ) } |