| Step | Hyp | Ref | Expression | 
						
							| 1 |  | efgval.w |  |-  W = ( _I ` Word ( I X. 2o ) ) | 
						
							| 2 |  | efgval.r |  |-  .~ = ( ~FG ` I ) | 
						
							| 3 |  | efgval2.m |  |-  M = ( y e. I , z e. 2o |-> <. y , ( 1o \ z ) >. ) | 
						
							| 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 ) ) | 
						
							| 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 | 1 2 3 4 5 6 | efgsval |  |-  ( ( A ++ <" B "> ) e. dom S -> ( S ` ( A ++ <" B "> ) ) = ( ( A ++ <" B "> ) ` ( ( # ` ( A ++ <" B "> ) ) - 1 ) ) ) | 
						
							| 8 |  | s1cl |  |-  ( B e. W -> <" B "> e. Word W ) | 
						
							| 9 |  | ccatlen |  |-  ( ( A e. Word W /\ <" B "> e. Word W ) -> ( # ` ( A ++ <" B "> ) ) = ( ( # ` A ) + ( # ` <" B "> ) ) ) | 
						
							| 10 | 8 9 | sylan2 |  |-  ( ( A e. Word W /\ B e. W ) -> ( # ` ( A ++ <" B "> ) ) = ( ( # ` A ) + ( # ` <" B "> ) ) ) | 
						
							| 11 |  | s1len |  |-  ( # ` <" B "> ) = 1 | 
						
							| 12 | 11 | oveq2i |  |-  ( ( # ` A ) + ( # ` <" B "> ) ) = ( ( # ` A ) + 1 ) | 
						
							| 13 | 10 12 | eqtrdi |  |-  ( ( A e. Word W /\ B e. W ) -> ( # ` ( A ++ <" B "> ) ) = ( ( # ` A ) + 1 ) ) | 
						
							| 14 | 13 | oveq1d |  |-  ( ( A e. Word W /\ B e. W ) -> ( ( # ` ( A ++ <" B "> ) ) - 1 ) = ( ( ( # ` A ) + 1 ) - 1 ) ) | 
						
							| 15 |  | lencl |  |-  ( A e. Word W -> ( # ` A ) e. NN0 ) | 
						
							| 16 | 15 | nn0cnd |  |-  ( A e. Word W -> ( # ` A ) e. CC ) | 
						
							| 17 |  | ax-1cn |  |-  1 e. CC | 
						
							| 18 |  | pncan |  |-  ( ( ( # ` A ) e. CC /\ 1 e. CC ) -> ( ( ( # ` A ) + 1 ) - 1 ) = ( # ` A ) ) | 
						
							| 19 | 16 17 18 | sylancl |  |-  ( A e. Word W -> ( ( ( # ` A ) + 1 ) - 1 ) = ( # ` A ) ) | 
						
							| 20 | 16 | addlidd |  |-  ( A e. Word W -> ( 0 + ( # ` A ) ) = ( # ` A ) ) | 
						
							| 21 | 19 20 | eqtr4d |  |-  ( A e. Word W -> ( ( ( # ` A ) + 1 ) - 1 ) = ( 0 + ( # ` A ) ) ) | 
						
							| 22 | 21 | adantr |  |-  ( ( A e. Word W /\ B e. W ) -> ( ( ( # ` A ) + 1 ) - 1 ) = ( 0 + ( # ` A ) ) ) | 
						
							| 23 | 14 22 | eqtrd |  |-  ( ( A e. Word W /\ B e. W ) -> ( ( # ` ( A ++ <" B "> ) ) - 1 ) = ( 0 + ( # ` A ) ) ) | 
						
							| 24 | 23 | fveq2d |  |-  ( ( A e. Word W /\ B e. W ) -> ( ( A ++ <" B "> ) ` ( ( # ` ( A ++ <" B "> ) ) - 1 ) ) = ( ( A ++ <" B "> ) ` ( 0 + ( # ` A ) ) ) ) | 
						
							| 25 |  | simpl |  |-  ( ( A e. Word W /\ B e. W ) -> A e. Word W ) | 
						
							| 26 | 8 | adantl |  |-  ( ( A e. Word W /\ B e. W ) -> <" B "> e. Word W ) | 
						
							| 27 |  | 1nn |  |-  1 e. NN | 
						
							| 28 | 11 27 | eqeltri |  |-  ( # ` <" B "> ) e. NN | 
						
							| 29 |  | lbfzo0 |  |-  ( 0 e. ( 0 ..^ ( # ` <" B "> ) ) <-> ( # ` <" B "> ) e. NN ) | 
						
							| 30 | 28 29 | mpbir |  |-  0 e. ( 0 ..^ ( # ` <" B "> ) ) | 
						
							| 31 | 30 | a1i |  |-  ( ( A e. Word W /\ B e. W ) -> 0 e. ( 0 ..^ ( # ` <" B "> ) ) ) | 
						
							| 32 |  | ccatval3 |  |-  ( ( A e. Word W /\ <" B "> e. Word W /\ 0 e. ( 0 ..^ ( # ` <" B "> ) ) ) -> ( ( A ++ <" B "> ) ` ( 0 + ( # ` A ) ) ) = ( <" B "> ` 0 ) ) | 
						
							| 33 | 25 26 31 32 | syl3anc |  |-  ( ( A e. Word W /\ B e. W ) -> ( ( A ++ <" B "> ) ` ( 0 + ( # ` A ) ) ) = ( <" B "> ` 0 ) ) | 
						
							| 34 |  | s1fv |  |-  ( B e. W -> ( <" B "> ` 0 ) = B ) | 
						
							| 35 | 34 | adantl |  |-  ( ( A e. Word W /\ B e. W ) -> ( <" B "> ` 0 ) = B ) | 
						
							| 36 | 24 33 35 | 3eqtrd |  |-  ( ( A e. Word W /\ B e. W ) -> ( ( A ++ <" B "> ) ` ( ( # ` ( A ++ <" B "> ) ) - 1 ) ) = B ) | 
						
							| 37 | 7 36 | sylan9eqr |  |-  ( ( ( A e. Word W /\ B e. W ) /\ ( A ++ <" B "> ) e. dom S ) -> ( S ` ( A ++ <" B "> ) ) = B ) | 
						
							| 38 | 37 | 3impa |  |-  ( ( A e. Word W /\ B e. W /\ ( A ++ <" B "> ) e. dom S ) -> ( S ` ( A ++ <" B "> ) ) = B ) |