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Description: If two words A , B are related under the free group equivalence, then there exist two extension sequences a , b such that a ends at A , b ends at B , and a and B have the same starting point. (Contributed by Mario Carneiro, 1-Oct-2015)
| Ref | Expression | ||
|---|---|---|---|
| Hypotheses | efgval.w | |- W = ( _I ` Word ( I X. 2o ) ) |
|
| efgval.r | |- .~ = ( ~FG ` I ) |
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| efgval2.m | |- M = ( y e. I , z e. 2o |-> <. y , ( 1o \ z ) >. ) |
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| efgval2.t | |- T = ( v e. W |-> ( n e. ( 0 ... ( # ` v ) ) , w e. ( I X. 2o ) |-> ( v splice <. n , n , <" w ( M ` w ) "> >. ) ) ) |
||
| efgred.d | |- D = ( W \ U_ x e. W ran ( T ` x ) ) |
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| efgred.s | |- S = ( m e. { t e. ( Word W \ { (/) } ) | ( ( t ` 0 ) e. D /\ A. k e. ( 1 ..^ ( # ` t ) ) ( t ` k ) e. ran ( T ` ( t ` ( k - 1 ) ) ) ) } |-> ( m ` ( ( # ` m ) - 1 ) ) ) |
||
| Assertion | efgrelex | |- ( A .~ B -> E. a e. ( `' S " { A } ) E. b e. ( `' S " { B } ) ( a ` 0 ) = ( b ` 0 ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | efgval.w | |- W = ( _I ` Word ( I X. 2o ) ) |
|
| 2 | efgval.r | |- .~ = ( ~FG ` I ) |
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| 3 | efgval2.m | |- M = ( y e. I , z e. 2o |-> <. y , ( 1o \ z ) >. ) |
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| 4 | efgval2.t | |- T = ( v e. W |-> ( n e. ( 0 ... ( # ` v ) ) , w e. ( I X. 2o ) |-> ( v splice <. n , n , <" w ( M ` w ) "> >. ) ) ) |
|
| 5 | efgred.d | |- D = ( W \ U_ x e. W ran ( T ` x ) ) |
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| 6 | efgred.s | |- S = ( m e. { t e. ( Word W \ { (/) } ) | ( ( t ` 0 ) e. D /\ A. k e. ( 1 ..^ ( # ` t ) ) ( t ` k ) e. ran ( T ` ( t ` ( k - 1 ) ) ) ) } |-> ( m ` ( ( # ` m ) - 1 ) ) ) |
|
| 7 | eqid | |- { <. i , j >. | E. c e. ( `' S " { i } ) E. d e. ( `' S " { j } ) ( c ` 0 ) = ( d ` 0 ) } = { <. i , j >. | E. c e. ( `' S " { i } ) E. d e. ( `' S " { j } ) ( c ` 0 ) = ( d ` 0 ) } |
|
| 8 | 1 2 3 4 5 6 7 | efgrelexlemb | |- .~ C_ { <. i , j >. | E. c e. ( `' S " { i } ) E. d e. ( `' S " { j } ) ( c ` 0 ) = ( d ` 0 ) } |
| 9 | 8 | ssbri | |- ( A .~ B -> A { <. i , j >. | E. c e. ( `' S " { i } ) E. d e. ( `' S " { j } ) ( c ` 0 ) = ( d ` 0 ) } B ) |
| 10 | 1 2 3 4 5 6 7 | efgrelexlema | |- ( A { <. i , j >. | E. c e. ( `' S " { i } ) E. d e. ( `' S " { j } ) ( c ` 0 ) = ( d ` 0 ) } B <-> E. a e. ( `' S " { A } ) E. b e. ( `' S " { B } ) ( a ` 0 ) = ( b ` 0 ) ) |
| 11 | 9 10 | sylib | |- ( A .~ B -> E. a e. ( `' S " { A } ) E. b e. ( `' S " { B } ) ( a ` 0 ) = ( b ` 0 ) ) |