| 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 |  | splfv1.x |  |-  ( ph -> X e. ( 0 ..^ F ) ) | 
						
							| 6 |  | 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 ) >. ) ) ) | 
						
							| 7 | 1 2 3 4 6 | syl13anc |  |-  ( ph -> ( S splice <. F , T , R >. ) = ( ( ( S prefix F ) ++ R ) ++ ( S substr <. T , ( # ` S ) >. ) ) ) | 
						
							| 8 | 7 | fveq1d |  |-  ( ph -> ( ( S splice <. F , T , R >. ) ` X ) = ( ( ( ( S prefix F ) ++ R ) ++ ( S substr <. T , ( # ` S ) >. ) ) ` X ) ) | 
						
							| 9 |  | pfxcl |  |-  ( S e. Word A -> ( S prefix F ) e. Word A ) | 
						
							| 10 | 1 9 | syl |  |-  ( ph -> ( S prefix F ) e. Word A ) | 
						
							| 11 |  | ccatcl |  |-  ( ( ( S prefix F ) e. Word A /\ R e. Word A ) -> ( ( S prefix F ) ++ R ) e. Word A ) | 
						
							| 12 | 10 4 11 | syl2anc |  |-  ( ph -> ( ( S prefix F ) ++ R ) e. Word A ) | 
						
							| 13 |  | swrdcl |  |-  ( S e. Word A -> ( S substr <. T , ( # ` S ) >. ) e. Word A ) | 
						
							| 14 | 1 13 | syl |  |-  ( ph -> ( S substr <. T , ( # ` S ) >. ) e. Word A ) | 
						
							| 15 | 2 | elfzelzd |  |-  ( ph -> F e. ZZ ) | 
						
							| 16 | 15 | uzidd |  |-  ( ph -> F e. ( ZZ>= ` F ) ) | 
						
							| 17 |  | lencl |  |-  ( R e. Word A -> ( # ` R ) e. NN0 ) | 
						
							| 18 | 4 17 | syl |  |-  ( ph -> ( # ` R ) e. NN0 ) | 
						
							| 19 |  | uzaddcl |  |-  ( ( F e. ( ZZ>= ` F ) /\ ( # ` R ) e. NN0 ) -> ( F + ( # ` R ) ) e. ( ZZ>= ` F ) ) | 
						
							| 20 | 16 18 19 | syl2anc |  |-  ( ph -> ( F + ( # ` R ) ) e. ( ZZ>= ` F ) ) | 
						
							| 21 |  | fzoss2 |  |-  ( ( F + ( # ` R ) ) e. ( ZZ>= ` F ) -> ( 0 ..^ F ) C_ ( 0 ..^ ( F + ( # ` R ) ) ) ) | 
						
							| 22 | 20 21 | syl |  |-  ( ph -> ( 0 ..^ F ) C_ ( 0 ..^ ( F + ( # ` R ) ) ) ) | 
						
							| 23 | 22 5 | sseldd |  |-  ( ph -> X e. ( 0 ..^ ( F + ( # ` R ) ) ) ) | 
						
							| 24 |  | ccatlen |  |-  ( ( ( S prefix F ) e. Word A /\ R e. Word A ) -> ( # ` ( ( S prefix F ) ++ R ) ) = ( ( # ` ( S prefix F ) ) + ( # ` R ) ) ) | 
						
							| 25 | 10 4 24 | syl2anc |  |-  ( ph -> ( # ` ( ( S prefix F ) ++ R ) ) = ( ( # ` ( S prefix F ) ) + ( # ` R ) ) ) | 
						
							| 26 |  | fzass4 |  |-  ( ( F e. ( 0 ... ( # ` S ) ) /\ T e. ( F ... ( # ` S ) ) ) <-> ( F e. ( 0 ... T ) /\ T e. ( 0 ... ( # ` S ) ) ) ) | 
						
							| 27 | 26 | biimpri |  |-  ( ( F e. ( 0 ... T ) /\ T e. ( 0 ... ( # ` S ) ) ) -> ( F e. ( 0 ... ( # ` S ) ) /\ T e. ( F ... ( # ` S ) ) ) ) | 
						
							| 28 | 27 | simpld |  |-  ( ( F e. ( 0 ... T ) /\ T e. ( 0 ... ( # ` S ) ) ) -> F e. ( 0 ... ( # ` S ) ) ) | 
						
							| 29 | 2 3 28 | syl2anc |  |-  ( ph -> F e. ( 0 ... ( # ` S ) ) ) | 
						
							| 30 |  | pfxlen |  |-  ( ( S e. Word A /\ F e. ( 0 ... ( # ` S ) ) ) -> ( # ` ( S prefix F ) ) = F ) | 
						
							| 31 | 1 29 30 | syl2anc |  |-  ( ph -> ( # ` ( S prefix F ) ) = F ) | 
						
							| 32 | 31 | oveq1d |  |-  ( ph -> ( ( # ` ( S prefix F ) ) + ( # ` R ) ) = ( F + ( # ` R ) ) ) | 
						
							| 33 | 25 32 | eqtrd |  |-  ( ph -> ( # ` ( ( S prefix F ) ++ R ) ) = ( F + ( # ` R ) ) ) | 
						
							| 34 | 33 | oveq2d |  |-  ( ph -> ( 0 ..^ ( # ` ( ( S prefix F ) ++ R ) ) ) = ( 0 ..^ ( F + ( # ` R ) ) ) ) | 
						
							| 35 | 23 34 | eleqtrrd |  |-  ( ph -> X e. ( 0 ..^ ( # ` ( ( S prefix F ) ++ R ) ) ) ) | 
						
							| 36 |  | ccatval1 |  |-  ( ( ( ( S prefix F ) ++ R ) e. Word A /\ ( S substr <. T , ( # ` S ) >. ) e. Word A /\ X e. ( 0 ..^ ( # ` ( ( S prefix F ) ++ R ) ) ) ) -> ( ( ( ( S prefix F ) ++ R ) ++ ( S substr <. T , ( # ` S ) >. ) ) ` X ) = ( ( ( S prefix F ) ++ R ) ` X ) ) | 
						
							| 37 | 12 14 35 36 | syl3anc |  |-  ( ph -> ( ( ( ( S prefix F ) ++ R ) ++ ( S substr <. T , ( # ` S ) >. ) ) ` X ) = ( ( ( S prefix F ) ++ R ) ` X ) ) | 
						
							| 38 | 31 | oveq2d |  |-  ( ph -> ( 0 ..^ ( # ` ( S prefix F ) ) ) = ( 0 ..^ F ) ) | 
						
							| 39 | 5 38 | eleqtrrd |  |-  ( ph -> X e. ( 0 ..^ ( # ` ( S prefix F ) ) ) ) | 
						
							| 40 |  | ccatval1 |  |-  ( ( ( S prefix F ) e. Word A /\ R e. Word A /\ X e. ( 0 ..^ ( # ` ( S prefix F ) ) ) ) -> ( ( ( S prefix F ) ++ R ) ` X ) = ( ( S prefix F ) ` X ) ) | 
						
							| 41 | 10 4 39 40 | syl3anc |  |-  ( ph -> ( ( ( S prefix F ) ++ R ) ` X ) = ( ( S prefix F ) ` X ) ) | 
						
							| 42 |  | pfxfv |  |-  ( ( S e. Word A /\ F e. ( 0 ... ( # ` S ) ) /\ X e. ( 0 ..^ F ) ) -> ( ( S prefix F ) ` X ) = ( S ` X ) ) | 
						
							| 43 | 1 29 5 42 | syl3anc |  |-  ( ph -> ( ( S prefix F ) ` X ) = ( S ` X ) ) | 
						
							| 44 | 41 43 | eqtrd |  |-  ( ph -> ( ( ( S prefix F ) ++ R ) ` X ) = ( S ` X ) ) | 
						
							| 45 | 8 37 44 | 3eqtrd |  |-  ( ph -> ( ( S splice <. F , T , R >. ) ` X ) = ( S ` X ) ) |