| Step | Hyp | Ref | Expression | 
						
							| 1 |  | spllen.s | ⊢ ( 𝜑  →  𝑆  ∈  Word  𝐴 ) | 
						
							| 2 |  | spllen.f | ⊢ ( 𝜑  →  𝐹  ∈  ( 0 ... 𝑇 ) ) | 
						
							| 3 |  | spllen.t | ⊢ ( 𝜑  →  𝑇  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 4 |  | spllen.r | ⊢ ( 𝜑  →  𝑅  ∈  Word  𝐴 ) | 
						
							| 5 |  | splfv1.x | ⊢ ( 𝜑  →  𝑋  ∈  ( 0 ..^ 𝐹 ) ) | 
						
							| 6 |  | 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 ) 〉 ) ) ) | 
						
							| 7 | 1 2 3 4 6 | syl13anc | ⊢ ( 𝜑  →  ( 𝑆  splice  〈 𝐹 ,  𝑇 ,  𝑅 〉 )  =  ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ) ) | 
						
							| 8 | 7 | fveq1d | ⊢ ( 𝜑  →  ( ( 𝑆  splice  〈 𝐹 ,  𝑇 ,  𝑅 〉 ) ‘ 𝑋 )  =  ( ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ) ‘ 𝑋 ) ) | 
						
							| 9 |  | pfxcl | ⊢ ( 𝑆  ∈  Word  𝐴  →  ( 𝑆  prefix  𝐹 )  ∈  Word  𝐴 ) | 
						
							| 10 | 1 9 | syl | ⊢ ( 𝜑  →  ( 𝑆  prefix  𝐹 )  ∈  Word  𝐴 ) | 
						
							| 11 |  | ccatcl | ⊢ ( ( ( 𝑆  prefix  𝐹 )  ∈  Word  𝐴  ∧  𝑅  ∈  Word  𝐴 )  →  ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ∈  Word  𝐴 ) | 
						
							| 12 | 10 4 11 | syl2anc | ⊢ ( 𝜑  →  ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ∈  Word  𝐴 ) | 
						
							| 13 |  | swrdcl | ⊢ ( 𝑆  ∈  Word  𝐴  →  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 )  ∈  Word  𝐴 ) | 
						
							| 14 | 1 13 | syl | ⊢ ( 𝜑  →  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 )  ∈  Word  𝐴 ) | 
						
							| 15 | 2 | elfzelzd | ⊢ ( 𝜑  →  𝐹  ∈  ℤ ) | 
						
							| 16 | 15 | uzidd | ⊢ ( 𝜑  →  𝐹  ∈  ( ℤ≥ ‘ 𝐹 ) ) | 
						
							| 17 |  | lencl | ⊢ ( 𝑅  ∈  Word  𝐴  →  ( ♯ ‘ 𝑅 )  ∈  ℕ0 ) | 
						
							| 18 | 4 17 | syl | ⊢ ( 𝜑  →  ( ♯ ‘ 𝑅 )  ∈  ℕ0 ) | 
						
							| 19 |  | uzaddcl | ⊢ ( ( 𝐹  ∈  ( ℤ≥ ‘ 𝐹 )  ∧  ( ♯ ‘ 𝑅 )  ∈  ℕ0 )  →  ( 𝐹  +  ( ♯ ‘ 𝑅 ) )  ∈  ( ℤ≥ ‘ 𝐹 ) ) | 
						
							| 20 | 16 18 19 | syl2anc | ⊢ ( 𝜑  →  ( 𝐹  +  ( ♯ ‘ 𝑅 ) )  ∈  ( ℤ≥ ‘ 𝐹 ) ) | 
						
							| 21 |  | fzoss2 | ⊢ ( ( 𝐹  +  ( ♯ ‘ 𝑅 ) )  ∈  ( ℤ≥ ‘ 𝐹 )  →  ( 0 ..^ 𝐹 )  ⊆  ( 0 ..^ ( 𝐹  +  ( ♯ ‘ 𝑅 ) ) ) ) | 
						
							| 22 | 20 21 | syl | ⊢ ( 𝜑  →  ( 0 ..^ 𝐹 )  ⊆  ( 0 ..^ ( 𝐹  +  ( ♯ ‘ 𝑅 ) ) ) ) | 
						
							| 23 | 22 5 | sseldd | ⊢ ( 𝜑  →  𝑋  ∈  ( 0 ..^ ( 𝐹  +  ( ♯ ‘ 𝑅 ) ) ) ) | 
						
							| 24 |  | ccatlen | ⊢ ( ( ( 𝑆  prefix  𝐹 )  ∈  Word  𝐴  ∧  𝑅  ∈  Word  𝐴 )  →  ( ♯ ‘ ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) )  =  ( ( ♯ ‘ ( 𝑆  prefix  𝐹 ) )  +  ( ♯ ‘ 𝑅 ) ) ) | 
						
							| 25 | 10 4 24 | syl2anc | ⊢ ( 𝜑  →  ( ♯ ‘ ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) )  =  ( ( ♯ ‘ ( 𝑆  prefix  𝐹 ) )  +  ( ♯ ‘ 𝑅 ) ) ) | 
						
							| 26 |  | fzass4 | ⊢ ( ( 𝐹  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) )  ∧  𝑇  ∈  ( 𝐹 ... ( ♯ ‘ 𝑆 ) ) )  ↔  ( 𝐹  ∈  ( 0 ... 𝑇 )  ∧  𝑇  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) ) | 
						
							| 27 | 26 | biimpri | ⊢ ( ( 𝐹  ∈  ( 0 ... 𝑇 )  ∧  𝑇  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) )  →  ( 𝐹  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) )  ∧  𝑇  ∈  ( 𝐹 ... ( ♯ ‘ 𝑆 ) ) ) ) | 
						
							| 28 | 27 | simpld | ⊢ ( ( 𝐹  ∈  ( 0 ... 𝑇 )  ∧  𝑇  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) )  →  𝐹  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 29 | 2 3 28 | syl2anc | ⊢ ( 𝜑  →  𝐹  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 30 |  | pfxlen | ⊢ ( ( 𝑆  ∈  Word  𝐴  ∧  𝐹  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) )  →  ( ♯ ‘ ( 𝑆  prefix  𝐹 ) )  =  𝐹 ) | 
						
							| 31 | 1 29 30 | syl2anc | ⊢ ( 𝜑  →  ( ♯ ‘ ( 𝑆  prefix  𝐹 ) )  =  𝐹 ) | 
						
							| 32 | 31 | oveq1d | ⊢ ( 𝜑  →  ( ( ♯ ‘ ( 𝑆  prefix  𝐹 ) )  +  ( ♯ ‘ 𝑅 ) )  =  ( 𝐹  +  ( ♯ ‘ 𝑅 ) ) ) | 
						
							| 33 | 25 32 | eqtrd | ⊢ ( 𝜑  →  ( ♯ ‘ ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) )  =  ( 𝐹  +  ( ♯ ‘ 𝑅 ) ) ) | 
						
							| 34 | 33 | oveq2d | ⊢ ( 𝜑  →  ( 0 ..^ ( ♯ ‘ ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) ) )  =  ( 0 ..^ ( 𝐹  +  ( ♯ ‘ 𝑅 ) ) ) ) | 
						
							| 35 | 23 34 | eleqtrrd | ⊢ ( 𝜑  →  𝑋  ∈  ( 0 ..^ ( ♯ ‘ ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) ) ) ) | 
						
							| 36 |  | ccatval1 | ⊢ ( ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ∈  Word  𝐴  ∧  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 )  ∈  Word  𝐴  ∧  𝑋  ∈  ( 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 | ⊢ ( 𝜑  →  ( ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ) ‘ 𝑋 )  =  ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) ‘ 𝑋 ) ) | 
						
							| 38 | 31 | oveq2d | ⊢ ( 𝜑  →  ( 0 ..^ ( ♯ ‘ ( 𝑆  prefix  𝐹 ) ) )  =  ( 0 ..^ 𝐹 ) ) | 
						
							| 39 | 5 38 | eleqtrrd | ⊢ ( 𝜑  →  𝑋  ∈  ( 0 ..^ ( ♯ ‘ ( 𝑆  prefix  𝐹 ) ) ) ) | 
						
							| 40 |  | ccatval1 | ⊢ ( ( ( 𝑆  prefix  𝐹 )  ∈  Word  𝐴  ∧  𝑅  ∈  Word  𝐴  ∧  𝑋  ∈  ( 0 ..^ ( ♯ ‘ ( 𝑆  prefix  𝐹 ) ) ) )  →  ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) ‘ 𝑋 )  =  ( ( 𝑆  prefix  𝐹 ) ‘ 𝑋 ) ) | 
						
							| 41 | 10 4 39 40 | syl3anc | ⊢ ( 𝜑  →  ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) ‘ 𝑋 )  =  ( ( 𝑆  prefix  𝐹 ) ‘ 𝑋 ) ) | 
						
							| 42 |  | pfxfv | ⊢ ( ( 𝑆  ∈  Word  𝐴  ∧  𝐹  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) )  ∧  𝑋  ∈  ( 0 ..^ 𝐹 ) )  →  ( ( 𝑆  prefix  𝐹 ) ‘ 𝑋 )  =  ( 𝑆 ‘ 𝑋 ) ) | 
						
							| 43 | 1 29 5 42 | syl3anc | ⊢ ( 𝜑  →  ( ( 𝑆  prefix  𝐹 ) ‘ 𝑋 )  =  ( 𝑆 ‘ 𝑋 ) ) | 
						
							| 44 | 41 43 | eqtrd | ⊢ ( 𝜑  →  ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 ) ‘ 𝑋 )  =  ( 𝑆 ‘ 𝑋 ) ) | 
						
							| 45 | 8 37 44 | 3eqtrd | ⊢ ( 𝜑  →  ( ( 𝑆  splice  〈 𝐹 ,  𝑇 ,  𝑅 〉 ) ‘ 𝑋 )  =  ( 𝑆 ‘ 𝑋 ) ) |