| Step | Hyp | Ref | Expression | 
						
							| 1 |  | splfv3.s | ⊢ ( 𝜑  →  𝑆  ∈  Word  𝐴 ) | 
						
							| 2 |  | splfv3.f | ⊢ ( 𝜑  →  𝐹  ∈  ( 0 ... 𝑇 ) ) | 
						
							| 3 |  | splfv3.t | ⊢ ( 𝜑  →  𝑇  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 4 |  | splfv3.r | ⊢ ( 𝜑  →  𝑅  ∈  Word  𝐴 ) | 
						
							| 5 |  | splfv3.x | ⊢ ( 𝜑  →  𝑋  ∈  ( 0 ..^ ( ( ♯ ‘ 𝑆 )  −  𝑇 ) ) ) | 
						
							| 6 |  | splfv3.k | ⊢ ( 𝜑  →  𝐾  =  ( 𝐹  +  ( ♯ ‘ 𝑅 ) ) ) | 
						
							| 7 |  | splval | ⊢ ( ( 𝑆  ∈  Word  𝐴  ∧  ( 𝐹  ∈  ( 0 ... 𝑇 )  ∧  𝑇  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) )  ∧  𝑅  ∈  Word  𝐴 ) )  →  ( 𝑆  splice  〈 𝐹 ,  𝑇 ,  𝑅 〉 )  =  ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ) ) | 
						
							| 8 | 1 2 3 4 7 | syl13anc | ⊢ ( 𝜑  →  ( 𝑆  splice  〈 𝐹 ,  𝑇 ,  𝑅 〉 )  =  ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ) ) | 
						
							| 9 |  | elfzuz3 | ⊢ ( 𝑇  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) )  →  ( ♯ ‘ 𝑆 )  ∈  ( ℤ≥ ‘ 𝑇 ) ) | 
						
							| 10 |  | fzss2 | ⊢ ( ( ♯ ‘ 𝑆 )  ∈  ( ℤ≥ ‘ 𝑇 )  →  ( 0 ... 𝑇 )  ⊆  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 11 | 3 9 10 | 3syl | ⊢ ( 𝜑  →  ( 0 ... 𝑇 )  ⊆  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 12 | 11 2 | sseldd | ⊢ ( 𝜑  →  𝐹  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 13 |  | pfxlen | ⊢ ( ( 𝑆  ∈  Word  𝐴  ∧  𝐹  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) )  →  ( ♯ ‘ ( 𝑆  prefix  𝐹 ) )  =  𝐹 ) | 
						
							| 14 | 1 12 13 | syl2anc | ⊢ ( 𝜑  →  ( ♯ ‘ ( 𝑆  prefix  𝐹 ) )  =  𝐹 ) | 
						
							| 15 | 14 | oveq1d | ⊢ ( 𝜑  →  ( ( ♯ ‘ ( 𝑆  prefix  𝐹 ) )  +  ( ♯ ‘ 𝑅 ) )  =  ( 𝐹  +  ( ♯ ‘ 𝑅 ) ) ) | 
						
							| 16 |  | pfxcl | ⊢ ( 𝑆  ∈  Word  𝐴  →  ( 𝑆  prefix  𝐹 )  ∈  Word  𝐴 ) | 
						
							| 17 | 1 16 | syl | ⊢ ( 𝜑  →  ( 𝑆  prefix  𝐹 )  ∈  Word  𝐴 ) | 
						
							| 18 |  | ccatlen | ⊢ ( ( ( 𝑆  prefix  𝐹 )  ∈  Word  𝐴  ∧  𝑅  ∈  Word  𝐴 )  →  ( ♯ ‘ ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) )  =  ( ( ♯ ‘ ( 𝑆  prefix  𝐹 ) )  +  ( ♯ ‘ 𝑅 ) ) ) | 
						
							| 19 | 17 4 18 | syl2anc | ⊢ ( 𝜑  →  ( ♯ ‘ ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) )  =  ( ( ♯ ‘ ( 𝑆  prefix  𝐹 ) )  +  ( ♯ ‘ 𝑅 ) ) ) | 
						
							| 20 | 15 19 6 | 3eqtr4rd | ⊢ ( 𝜑  →  𝐾  =  ( ♯ ‘ ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) ) ) | 
						
							| 21 | 20 | oveq2d | ⊢ ( 𝜑  →  ( 𝑋  +  𝐾 )  =  ( 𝑋  +  ( ♯ ‘ ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) ) ) ) | 
						
							| 22 | 8 21 | fveq12d | ⊢ ( 𝜑  →  ( ( 𝑆  splice  〈 𝐹 ,  𝑇 ,  𝑅 〉 ) ‘ ( 𝑋  +  𝐾 ) )  =  ( ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ) ‘ ( 𝑋  +  ( ♯ ‘ ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) ) ) ) ) | 
						
							| 23 |  | ccatcl | ⊢ ( ( ( 𝑆  prefix  𝐹 )  ∈  Word  𝐴  ∧  𝑅  ∈  Word  𝐴 )  →  ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ∈  Word  𝐴 ) | 
						
							| 24 | 17 4 23 | syl2anc | ⊢ ( 𝜑  →  ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ∈  Word  𝐴 ) | 
						
							| 25 |  | swrdcl | ⊢ ( 𝑆  ∈  Word  𝐴  →  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 )  ∈  Word  𝐴 ) | 
						
							| 26 | 1 25 | syl | ⊢ ( 𝜑  →  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 )  ∈  Word  𝐴 ) | 
						
							| 27 |  | lencl | ⊢ ( 𝑆  ∈  Word  𝐴  →  ( ♯ ‘ 𝑆 )  ∈  ℕ0 ) | 
						
							| 28 |  | nn0fz0 | ⊢ ( ( ♯ ‘ 𝑆 )  ∈  ℕ0  ↔  ( ♯ ‘ 𝑆 )  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 29 | 27 28 | sylib | ⊢ ( 𝑆  ∈  Word  𝐴  →  ( ♯ ‘ 𝑆 )  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 30 | 1 29 | syl | ⊢ ( 𝜑  →  ( ♯ ‘ 𝑆 )  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 31 |  | swrdlen | ⊢ ( ( 𝑆  ∈  Word  𝐴  ∧  𝑇  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) )  ∧  ( ♯ ‘ 𝑆 )  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) )  →  ( ♯ ‘ ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) )  =  ( ( ♯ ‘ 𝑆 )  −  𝑇 ) ) | 
						
							| 32 | 1 3 30 31 | syl3anc | ⊢ ( 𝜑  →  ( ♯ ‘ ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) )  =  ( ( ♯ ‘ 𝑆 )  −  𝑇 ) ) | 
						
							| 33 | 32 | oveq2d | ⊢ ( 𝜑  →  ( 0 ..^ ( ♯ ‘ ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ) )  =  ( 0 ..^ ( ( ♯ ‘ 𝑆 )  −  𝑇 ) ) ) | 
						
							| 34 | 5 33 | eleqtrrd | ⊢ ( 𝜑  →  𝑋  ∈  ( 0 ..^ ( ♯ ‘ ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ) ) ) | 
						
							| 35 |  | ccatval3 | ⊢ ( ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ∈  Word  𝐴  ∧  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 )  ∈  Word  𝐴  ∧  𝑋  ∈  ( 0 ..^ ( ♯ ‘ ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ) ) )  →  ( ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ) ‘ ( 𝑋  +  ( ♯ ‘ ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) ) ) )  =  ( ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ‘ 𝑋 ) ) | 
						
							| 36 | 24 26 34 35 | syl3anc | ⊢ ( 𝜑  →  ( ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ) ‘ ( 𝑋  +  ( ♯ ‘ ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) ) ) )  =  ( ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ‘ 𝑋 ) ) | 
						
							| 37 |  | swrdfv | ⊢ ( ( ( 𝑆  ∈  Word  𝐴  ∧  𝑇  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) )  ∧  ( ♯ ‘ 𝑆 )  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) )  ∧  𝑋  ∈  ( 0 ..^ ( ( ♯ ‘ 𝑆 )  −  𝑇 ) ) )  →  ( ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ‘ 𝑋 )  =  ( 𝑆 ‘ ( 𝑋  +  𝑇 ) ) ) | 
						
							| 38 | 1 3 30 5 37 | syl31anc | ⊢ ( 𝜑  →  ( ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ‘ 𝑋 )  =  ( 𝑆 ‘ ( 𝑋  +  𝑇 ) ) ) | 
						
							| 39 | 22 36 38 | 3eqtrd | ⊢ ( 𝜑  →  ( ( 𝑆  splice  〈 𝐹 ,  𝑇 ,  𝑅 〉 ) ‘ ( 𝑋  +  𝐾 ) )  =  ( 𝑆 ‘ ( 𝑋  +  𝑇 ) ) ) |