| Step | Hyp | Ref | Expression | 
						
							| 1 |  | difeq2 |  |-  ( x = y -> ( X \ x ) = ( X \ y ) ) | 
						
							| 2 | 1 | breq1d |  |-  ( x = y -> ( ( X \ x ) ~< X <-> ( X \ y ) ~< X ) ) | 
						
							| 3 | 2 | elrab |  |-  ( y e. { x e. ~P X | ( X \ x ) ~< X } <-> ( y e. ~P X /\ ( X \ y ) ~< X ) ) | 
						
							| 4 |  | velpw |  |-  ( y e. ~P X <-> y C_ X ) | 
						
							| 5 | 4 | anbi1i |  |-  ( ( y e. ~P X /\ ( X \ y ) ~< X ) <-> ( y C_ X /\ ( X \ y ) ~< X ) ) | 
						
							| 6 | 3 5 | bitri |  |-  ( y e. { x e. ~P X | ( X \ x ) ~< X } <-> ( y C_ X /\ ( X \ y ) ~< X ) ) | 
						
							| 7 | 6 | a1i |  |-  ( ( X e. dom card /\ _om ~<_ X ) -> ( y e. { x e. ~P X | ( X \ x ) ~< X } <-> ( y C_ X /\ ( X \ y ) ~< X ) ) ) | 
						
							| 8 |  | simpl |  |-  ( ( X e. dom card /\ _om ~<_ X ) -> X e. dom card ) | 
						
							| 9 |  | difid |  |-  ( X \ X ) = (/) | 
						
							| 10 |  | infn0 |  |-  ( _om ~<_ X -> X =/= (/) ) | 
						
							| 11 | 10 | adantl |  |-  ( ( X e. dom card /\ _om ~<_ X ) -> X =/= (/) ) | 
						
							| 12 |  | 0sdomg |  |-  ( X e. dom card -> ( (/) ~< X <-> X =/= (/) ) ) | 
						
							| 13 | 12 | adantr |  |-  ( ( X e. dom card /\ _om ~<_ X ) -> ( (/) ~< X <-> X =/= (/) ) ) | 
						
							| 14 | 11 13 | mpbird |  |-  ( ( X e. dom card /\ _om ~<_ X ) -> (/) ~< X ) | 
						
							| 15 | 9 14 | eqbrtrid |  |-  ( ( X e. dom card /\ _om ~<_ X ) -> ( X \ X ) ~< X ) | 
						
							| 16 |  | difeq2 |  |-  ( y = X -> ( X \ y ) = ( X \ X ) ) | 
						
							| 17 | 16 | breq1d |  |-  ( y = X -> ( ( X \ y ) ~< X <-> ( X \ X ) ~< X ) ) | 
						
							| 18 | 17 | sbcieg |  |-  ( X e. dom card -> ( [. X / y ]. ( X \ y ) ~< X <-> ( X \ X ) ~< X ) ) | 
						
							| 19 | 18 | adantr |  |-  ( ( X e. dom card /\ _om ~<_ X ) -> ( [. X / y ]. ( X \ y ) ~< X <-> ( X \ X ) ~< X ) ) | 
						
							| 20 | 15 19 | mpbird |  |-  ( ( X e. dom card /\ _om ~<_ X ) -> [. X / y ]. ( X \ y ) ~< X ) | 
						
							| 21 |  | sdomirr |  |-  -. X ~< X | 
						
							| 22 |  | 0ex |  |-  (/) e. _V | 
						
							| 23 |  | difeq2 |  |-  ( y = (/) -> ( X \ y ) = ( X \ (/) ) ) | 
						
							| 24 |  | dif0 |  |-  ( X \ (/) ) = X | 
						
							| 25 | 23 24 | eqtrdi |  |-  ( y = (/) -> ( X \ y ) = X ) | 
						
							| 26 | 25 | breq1d |  |-  ( y = (/) -> ( ( X \ y ) ~< X <-> X ~< X ) ) | 
						
							| 27 | 22 26 | sbcie |  |-  ( [. (/) / y ]. ( X \ y ) ~< X <-> X ~< X ) | 
						
							| 28 | 27 | a1i |  |-  ( ( X e. dom card /\ _om ~<_ X ) -> ( [. (/) / y ]. ( X \ y ) ~< X <-> X ~< X ) ) | 
						
							| 29 | 21 28 | mtbiri |  |-  ( ( X e. dom card /\ _om ~<_ X ) -> -. [. (/) / y ]. ( X \ y ) ~< X ) | 
						
							| 30 |  | simp1l |  |-  ( ( ( X e. dom card /\ _om ~<_ X ) /\ z C_ X /\ w C_ z ) -> X e. dom card ) | 
						
							| 31 | 30 | difexd |  |-  ( ( ( X e. dom card /\ _om ~<_ X ) /\ z C_ X /\ w C_ z ) -> ( X \ w ) e. _V ) | 
						
							| 32 |  | sscon |  |-  ( w C_ z -> ( X \ z ) C_ ( X \ w ) ) | 
						
							| 33 | 32 | 3ad2ant3 |  |-  ( ( ( X e. dom card /\ _om ~<_ X ) /\ z C_ X /\ w C_ z ) -> ( X \ z ) C_ ( X \ w ) ) | 
						
							| 34 |  | ssdomg |  |-  ( ( X \ w ) e. _V -> ( ( X \ z ) C_ ( X \ w ) -> ( X \ z ) ~<_ ( X \ w ) ) ) | 
						
							| 35 | 31 33 34 | sylc |  |-  ( ( ( X e. dom card /\ _om ~<_ X ) /\ z C_ X /\ w C_ z ) -> ( X \ z ) ~<_ ( X \ w ) ) | 
						
							| 36 |  | domsdomtr |  |-  ( ( ( X \ z ) ~<_ ( X \ w ) /\ ( X \ w ) ~< X ) -> ( X \ z ) ~< X ) | 
						
							| 37 | 36 | ex |  |-  ( ( X \ z ) ~<_ ( X \ w ) -> ( ( X \ w ) ~< X -> ( X \ z ) ~< X ) ) | 
						
							| 38 | 35 37 | syl |  |-  ( ( ( X e. dom card /\ _om ~<_ X ) /\ z C_ X /\ w C_ z ) -> ( ( X \ w ) ~< X -> ( X \ z ) ~< X ) ) | 
						
							| 39 |  | vex |  |-  w e. _V | 
						
							| 40 |  | difeq2 |  |-  ( y = w -> ( X \ y ) = ( X \ w ) ) | 
						
							| 41 | 40 | breq1d |  |-  ( y = w -> ( ( X \ y ) ~< X <-> ( X \ w ) ~< X ) ) | 
						
							| 42 | 39 41 | sbcie |  |-  ( [. w / y ]. ( X \ y ) ~< X <-> ( X \ w ) ~< X ) | 
						
							| 43 |  | vex |  |-  z e. _V | 
						
							| 44 |  | difeq2 |  |-  ( y = z -> ( X \ y ) = ( X \ z ) ) | 
						
							| 45 | 44 | breq1d |  |-  ( y = z -> ( ( X \ y ) ~< X <-> ( X \ z ) ~< X ) ) | 
						
							| 46 | 43 45 | sbcie |  |-  ( [. z / y ]. ( X \ y ) ~< X <-> ( X \ z ) ~< X ) | 
						
							| 47 | 38 42 46 | 3imtr4g |  |-  ( ( ( X e. dom card /\ _om ~<_ X ) /\ z C_ X /\ w C_ z ) -> ( [. w / y ]. ( X \ y ) ~< X -> [. z / y ]. ( X \ y ) ~< X ) ) | 
						
							| 48 |  | infunsdom |  |-  ( ( ( X e. dom card /\ _om ~<_ X ) /\ ( ( X \ z ) ~< X /\ ( X \ w ) ~< X ) ) -> ( ( X \ z ) u. ( X \ w ) ) ~< X ) | 
						
							| 49 | 48 | ex |  |-  ( ( X e. dom card /\ _om ~<_ X ) -> ( ( ( X \ z ) ~< X /\ ( X \ w ) ~< X ) -> ( ( X \ z ) u. ( X \ w ) ) ~< X ) ) | 
						
							| 50 |  | difindi |  |-  ( X \ ( z i^i w ) ) = ( ( X \ z ) u. ( X \ w ) ) | 
						
							| 51 | 50 | breq1i |  |-  ( ( X \ ( z i^i w ) ) ~< X <-> ( ( X \ z ) u. ( X \ w ) ) ~< X ) | 
						
							| 52 | 49 51 | imbitrrdi |  |-  ( ( X e. dom card /\ _om ~<_ X ) -> ( ( ( X \ z ) ~< X /\ ( X \ w ) ~< X ) -> ( X \ ( z i^i w ) ) ~< X ) ) | 
						
							| 53 | 52 | 3ad2ant1 |  |-  ( ( ( X e. dom card /\ _om ~<_ X ) /\ z C_ X /\ w C_ X ) -> ( ( ( X \ z ) ~< X /\ ( X \ w ) ~< X ) -> ( X \ ( z i^i w ) ) ~< X ) ) | 
						
							| 54 | 46 42 | anbi12i |  |-  ( ( [. z / y ]. ( X \ y ) ~< X /\ [. w / y ]. ( X \ y ) ~< X ) <-> ( ( X \ z ) ~< X /\ ( X \ w ) ~< X ) ) | 
						
							| 55 | 43 | inex1 |  |-  ( z i^i w ) e. _V | 
						
							| 56 |  | difeq2 |  |-  ( y = ( z i^i w ) -> ( X \ y ) = ( X \ ( z i^i w ) ) ) | 
						
							| 57 | 56 | breq1d |  |-  ( y = ( z i^i w ) -> ( ( X \ y ) ~< X <-> ( X \ ( z i^i w ) ) ~< X ) ) | 
						
							| 58 | 55 57 | sbcie |  |-  ( [. ( z i^i w ) / y ]. ( X \ y ) ~< X <-> ( X \ ( z i^i w ) ) ~< X ) | 
						
							| 59 | 53 54 58 | 3imtr4g |  |-  ( ( ( X e. dom card /\ _om ~<_ X ) /\ z C_ X /\ w C_ X ) -> ( ( [. z / y ]. ( X \ y ) ~< X /\ [. w / y ]. ( X \ y ) ~< X ) -> [. ( z i^i w ) / y ]. ( X \ y ) ~< X ) ) | 
						
							| 60 | 7 8 20 29 47 59 | isfild |  |-  ( ( X e. dom card /\ _om ~<_ X ) -> { x e. ~P X | ( X \ x ) ~< X } e. ( Fil ` X ) ) |