| Step | Hyp | Ref | Expression | 
						
							| 1 |  | spllen.s |  |-  ( ph -> S e. Word A ) | 
						
							| 2 |  | spllen.f |  |-  ( ph -> F e. ( 0 ... T ) ) | 
						
							| 3 |  | spllen.t |  |-  ( ph -> T e. ( 0 ... ( # ` S ) ) ) | 
						
							| 4 |  | spllen.r |  |-  ( ph -> R e. Word A ) | 
						
							| 5 |  | splval |  |-  ( ( S e. Word A /\ ( F e. ( 0 ... T ) /\ T e. ( 0 ... ( # ` S ) ) /\ R e. Word A ) ) -> ( S splice <. F , T , R >. ) = ( ( ( S prefix F ) ++ R ) ++ ( S substr <. T , ( # ` S ) >. ) ) ) | 
						
							| 6 | 1 2 3 4 5 | syl13anc |  |-  ( ph -> ( S splice <. F , T , R >. ) = ( ( ( S prefix F ) ++ R ) ++ ( S substr <. T , ( # ` S ) >. ) ) ) | 
						
							| 7 | 6 | fveq2d |  |-  ( ph -> ( # ` ( S splice <. F , T , R >. ) ) = ( # ` ( ( ( S prefix F ) ++ R ) ++ ( S substr <. T , ( # ` S ) >. ) ) ) ) | 
						
							| 8 |  | pfxcl |  |-  ( S e. Word A -> ( S prefix F ) e. Word A ) | 
						
							| 9 | 1 8 | syl |  |-  ( ph -> ( S prefix F ) e. Word A ) | 
						
							| 10 |  | ccatcl |  |-  ( ( ( S prefix F ) e. Word A /\ R e. Word A ) -> ( ( S prefix F ) ++ R ) e. Word A ) | 
						
							| 11 | 9 4 10 | syl2anc |  |-  ( ph -> ( ( S prefix F ) ++ R ) e. Word A ) | 
						
							| 12 |  | swrdcl |  |-  ( S e. Word A -> ( S substr <. T , ( # ` S ) >. ) e. Word A ) | 
						
							| 13 | 1 12 | syl |  |-  ( ph -> ( S substr <. T , ( # ` S ) >. ) e. Word A ) | 
						
							| 14 |  | ccatlen |  |-  ( ( ( ( S prefix F ) ++ R ) e. Word A /\ ( S substr <. T , ( # ` S ) >. ) e. Word A ) -> ( # ` ( ( ( S prefix F ) ++ R ) ++ ( S substr <. T , ( # ` S ) >. ) ) ) = ( ( # ` ( ( S prefix F ) ++ R ) ) + ( # ` ( S substr <. T , ( # ` S ) >. ) ) ) ) | 
						
							| 15 | 11 13 14 | syl2anc |  |-  ( ph -> ( # ` ( ( ( S prefix F ) ++ R ) ++ ( S substr <. T , ( # ` S ) >. ) ) ) = ( ( # ` ( ( S prefix F ) ++ R ) ) + ( # ` ( S substr <. T , ( # ` S ) >. ) ) ) ) | 
						
							| 16 |  | lencl |  |-  ( R e. Word A -> ( # ` R ) e. NN0 ) | 
						
							| 17 | 16 | nn0cnd |  |-  ( R e. Word A -> ( # ` R ) e. CC ) | 
						
							| 18 | 4 17 | syl |  |-  ( ph -> ( # ` R ) e. CC ) | 
						
							| 19 |  | elfzelz |  |-  ( F e. ( 0 ... T ) -> F e. ZZ ) | 
						
							| 20 | 19 | zcnd |  |-  ( F e. ( 0 ... T ) -> F e. CC ) | 
						
							| 21 | 2 20 | syl |  |-  ( ph -> F e. CC ) | 
						
							| 22 | 18 21 | addcld |  |-  ( ph -> ( ( # ` R ) + F ) e. CC ) | 
						
							| 23 |  | elfzel2 |  |-  ( T e. ( 0 ... ( # ` S ) ) -> ( # ` S ) e. ZZ ) | 
						
							| 24 | 23 | zcnd |  |-  ( T e. ( 0 ... ( # ` S ) ) -> ( # ` S ) e. CC ) | 
						
							| 25 | 3 24 | syl |  |-  ( ph -> ( # ` S ) e. CC ) | 
						
							| 26 |  | elfzelz |  |-  ( T e. ( 0 ... ( # ` S ) ) -> T e. ZZ ) | 
						
							| 27 | 26 | zcnd |  |-  ( T e. ( 0 ... ( # ` S ) ) -> T e. CC ) | 
						
							| 28 | 3 27 | syl |  |-  ( ph -> T e. CC ) | 
						
							| 29 | 22 25 28 | addsub12d |  |-  ( ph -> ( ( ( # ` R ) + F ) + ( ( # ` S ) - T ) ) = ( ( # ` S ) + ( ( ( # ` R ) + F ) - T ) ) ) | 
						
							| 30 |  | ccatlen |  |-  ( ( ( S prefix F ) e. Word A /\ R e. Word A ) -> ( # ` ( ( S prefix F ) ++ R ) ) = ( ( # ` ( S prefix F ) ) + ( # ` R ) ) ) | 
						
							| 31 | 9 4 30 | syl2anc |  |-  ( ph -> ( # ` ( ( S prefix F ) ++ R ) ) = ( ( # ` ( S prefix F ) ) + ( # ` R ) ) ) | 
						
							| 32 |  | elfzuz |  |-  ( F e. ( 0 ... T ) -> F e. ( ZZ>= ` 0 ) ) | 
						
							| 33 | 2 32 | syl |  |-  ( ph -> F e. ( ZZ>= ` 0 ) ) | 
						
							| 34 |  | elfzuz3 |  |-  ( T e. ( 0 ... ( # ` S ) ) -> ( # ` S ) e. ( ZZ>= ` T ) ) | 
						
							| 35 | 3 34 | syl |  |-  ( ph -> ( # ` S ) e. ( ZZ>= ` T ) ) | 
						
							| 36 |  | elfzuz3 |  |-  ( F e. ( 0 ... T ) -> T e. ( ZZ>= ` F ) ) | 
						
							| 37 | 2 36 | syl |  |-  ( ph -> T e. ( ZZ>= ` F ) ) | 
						
							| 38 |  | uztrn |  |-  ( ( ( # ` S ) e. ( ZZ>= ` T ) /\ T e. ( ZZ>= ` F ) ) -> ( # ` S ) e. ( ZZ>= ` F ) ) | 
						
							| 39 | 35 37 38 | syl2anc |  |-  ( ph -> ( # ` S ) e. ( ZZ>= ` F ) ) | 
						
							| 40 |  | elfzuzb |  |-  ( F e. ( 0 ... ( # ` S ) ) <-> ( F e. ( ZZ>= ` 0 ) /\ ( # ` S ) e. ( ZZ>= ` F ) ) ) | 
						
							| 41 | 33 39 40 | sylanbrc |  |-  ( ph -> F e. ( 0 ... ( # ` S ) ) ) | 
						
							| 42 |  | pfxlen |  |-  ( ( S e. Word A /\ F e. ( 0 ... ( # ` S ) ) ) -> ( # ` ( S prefix F ) ) = F ) | 
						
							| 43 | 1 41 42 | syl2anc |  |-  ( ph -> ( # ` ( S prefix F ) ) = F ) | 
						
							| 44 | 43 | oveq1d |  |-  ( ph -> ( ( # ` ( S prefix F ) ) + ( # ` R ) ) = ( F + ( # ` R ) ) ) | 
						
							| 45 | 21 18 | addcomd |  |-  ( ph -> ( F + ( # ` R ) ) = ( ( # ` R ) + F ) ) | 
						
							| 46 | 31 44 45 | 3eqtrd |  |-  ( ph -> ( # ` ( ( S prefix F ) ++ R ) ) = ( ( # ` R ) + F ) ) | 
						
							| 47 |  | elfzuz2 |  |-  ( T e. ( 0 ... ( # ` S ) ) -> ( # ` S ) e. ( ZZ>= ` 0 ) ) | 
						
							| 48 |  | eluzfz2 |  |-  ( ( # ` S ) e. ( ZZ>= ` 0 ) -> ( # ` S ) e. ( 0 ... ( # ` S ) ) ) | 
						
							| 49 | 3 47 48 | 3syl |  |-  ( ph -> ( # ` S ) e. ( 0 ... ( # ` S ) ) ) | 
						
							| 50 |  | swrdlen |  |-  ( ( S e. Word A /\ T e. ( 0 ... ( # ` S ) ) /\ ( # ` S ) e. ( 0 ... ( # ` S ) ) ) -> ( # ` ( S substr <. T , ( # ` S ) >. ) ) = ( ( # ` S ) - T ) ) | 
						
							| 51 | 1 3 49 50 | syl3anc |  |-  ( ph -> ( # ` ( S substr <. T , ( # ` S ) >. ) ) = ( ( # ` S ) - T ) ) | 
						
							| 52 | 46 51 | oveq12d |  |-  ( ph -> ( ( # ` ( ( S prefix F ) ++ R ) ) + ( # ` ( S substr <. T , ( # ` S ) >. ) ) ) = ( ( ( # ` R ) + F ) + ( ( # ` S ) - T ) ) ) | 
						
							| 53 | 18 28 21 | subsub3d |  |-  ( ph -> ( ( # ` R ) - ( T - F ) ) = ( ( ( # ` R ) + F ) - T ) ) | 
						
							| 54 | 53 | oveq2d |  |-  ( ph -> ( ( # ` S ) + ( ( # ` R ) - ( T - F ) ) ) = ( ( # ` S ) + ( ( ( # ` R ) + F ) - T ) ) ) | 
						
							| 55 | 29 52 54 | 3eqtr4d |  |-  ( ph -> ( ( # ` ( ( S prefix F ) ++ R ) ) + ( # ` ( S substr <. T , ( # ` S ) >. ) ) ) = ( ( # ` S ) + ( ( # ` R ) - ( T - F ) ) ) ) | 
						
							| 56 | 7 15 55 | 3eqtrd |  |-  ( ph -> ( # ` ( S splice <. F , T , R >. ) ) = ( ( # ` S ) + ( ( # ` R ) - ( T - F ) ) ) ) |