| Step | Hyp | Ref | Expression | 
						
							| 1 |  | splval2.a | ⊢ ( 𝜑  →  𝐴  ∈  Word  𝑋 ) | 
						
							| 2 |  | splval2.b | ⊢ ( 𝜑  →  𝐵  ∈  Word  𝑋 ) | 
						
							| 3 |  | splval2.c | ⊢ ( 𝜑  →  𝐶  ∈  Word  𝑋 ) | 
						
							| 4 |  | splval2.r | ⊢ ( 𝜑  →  𝑅  ∈  Word  𝑋 ) | 
						
							| 5 |  | splval2.s | ⊢ ( 𝜑  →  𝑆  =  ( ( 𝐴  ++  𝐵 )  ++  𝐶 ) ) | 
						
							| 6 |  | splval2.f | ⊢ ( 𝜑  →  𝐹  =  ( ♯ ‘ 𝐴 ) ) | 
						
							| 7 |  | splval2.t | ⊢ ( 𝜑  →  𝑇  =  ( 𝐹  +  ( ♯ ‘ 𝐵 ) ) ) | 
						
							| 8 |  | ccatcl | ⊢ ( ( 𝐴  ∈  Word  𝑋  ∧  𝐵  ∈  Word  𝑋 )  →  ( 𝐴  ++  𝐵 )  ∈  Word  𝑋 ) | 
						
							| 9 | 1 2 8 | syl2anc | ⊢ ( 𝜑  →  ( 𝐴  ++  𝐵 )  ∈  Word  𝑋 ) | 
						
							| 10 |  | ccatcl | ⊢ ( ( ( 𝐴  ++  𝐵 )  ∈  Word  𝑋  ∧  𝐶  ∈  Word  𝑋 )  →  ( ( 𝐴  ++  𝐵 )  ++  𝐶 )  ∈  Word  𝑋 ) | 
						
							| 11 | 9 3 10 | syl2anc | ⊢ ( 𝜑  →  ( ( 𝐴  ++  𝐵 )  ++  𝐶 )  ∈  Word  𝑋 ) | 
						
							| 12 | 5 11 | eqeltrd | ⊢ ( 𝜑  →  𝑆  ∈  Word  𝑋 ) | 
						
							| 13 |  | lencl | ⊢ ( 𝐴  ∈  Word  𝑋  →  ( ♯ ‘ 𝐴 )  ∈  ℕ0 ) | 
						
							| 14 | 1 13 | syl | ⊢ ( 𝜑  →  ( ♯ ‘ 𝐴 )  ∈  ℕ0 ) | 
						
							| 15 | 6 14 | eqeltrd | ⊢ ( 𝜑  →  𝐹  ∈  ℕ0 ) | 
						
							| 16 |  | lencl | ⊢ ( 𝐵  ∈  Word  𝑋  →  ( ♯ ‘ 𝐵 )  ∈  ℕ0 ) | 
						
							| 17 | 2 16 | syl | ⊢ ( 𝜑  →  ( ♯ ‘ 𝐵 )  ∈  ℕ0 ) | 
						
							| 18 | 15 17 | nn0addcld | ⊢ ( 𝜑  →  ( 𝐹  +  ( ♯ ‘ 𝐵 ) )  ∈  ℕ0 ) | 
						
							| 19 | 7 18 | eqeltrd | ⊢ ( 𝜑  →  𝑇  ∈  ℕ0 ) | 
						
							| 20 |  | splval | ⊢ ( ( 𝑆  ∈  Word  𝑋  ∧  ( 𝐹  ∈  ℕ0  ∧  𝑇  ∈  ℕ0  ∧  𝑅  ∈  Word  𝑋 ) )  →  ( 𝑆  splice  〈 𝐹 ,  𝑇 ,  𝑅 〉 )  =  ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ) ) | 
						
							| 21 | 12 15 19 4 20 | syl13anc | ⊢ ( 𝜑  →  ( 𝑆  splice  〈 𝐹 ,  𝑇 ,  𝑅 〉 )  =  ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) ) ) | 
						
							| 22 |  | nn0uz | ⊢ ℕ0  =  ( ℤ≥ ‘ 0 ) | 
						
							| 23 | 15 22 | eleqtrdi | ⊢ ( 𝜑  →  𝐹  ∈  ( ℤ≥ ‘ 0 ) ) | 
						
							| 24 | 15 | nn0zd | ⊢ ( 𝜑  →  𝐹  ∈  ℤ ) | 
						
							| 25 | 24 | uzidd | ⊢ ( 𝜑  →  𝐹  ∈  ( ℤ≥ ‘ 𝐹 ) ) | 
						
							| 26 |  | uzaddcl | ⊢ ( ( 𝐹  ∈  ( ℤ≥ ‘ 𝐹 )  ∧  ( ♯ ‘ 𝐵 )  ∈  ℕ0 )  →  ( 𝐹  +  ( ♯ ‘ 𝐵 ) )  ∈  ( ℤ≥ ‘ 𝐹 ) ) | 
						
							| 27 | 25 17 26 | syl2anc | ⊢ ( 𝜑  →  ( 𝐹  +  ( ♯ ‘ 𝐵 ) )  ∈  ( ℤ≥ ‘ 𝐹 ) ) | 
						
							| 28 | 7 27 | eqeltrd | ⊢ ( 𝜑  →  𝑇  ∈  ( ℤ≥ ‘ 𝐹 ) ) | 
						
							| 29 |  | elfzuzb | ⊢ ( 𝐹  ∈  ( 0 ... 𝑇 )  ↔  ( 𝐹  ∈  ( ℤ≥ ‘ 0 )  ∧  𝑇  ∈  ( ℤ≥ ‘ 𝐹 ) ) ) | 
						
							| 30 | 23 28 29 | sylanbrc | ⊢ ( 𝜑  →  𝐹  ∈  ( 0 ... 𝑇 ) ) | 
						
							| 31 | 19 22 | eleqtrdi | ⊢ ( 𝜑  →  𝑇  ∈  ( ℤ≥ ‘ 0 ) ) | 
						
							| 32 |  | ccatlen | ⊢ ( ( ( 𝐴  ++  𝐵 )  ∈  Word  𝑋  ∧  𝐶  ∈  Word  𝑋 )  →  ( ♯ ‘ ( ( 𝐴  ++  𝐵 )  ++  𝐶 ) )  =  ( ( ♯ ‘ ( 𝐴  ++  𝐵 ) )  +  ( ♯ ‘ 𝐶 ) ) ) | 
						
							| 33 | 9 3 32 | syl2anc | ⊢ ( 𝜑  →  ( ♯ ‘ ( ( 𝐴  ++  𝐵 )  ++  𝐶 ) )  =  ( ( ♯ ‘ ( 𝐴  ++  𝐵 ) )  +  ( ♯ ‘ 𝐶 ) ) ) | 
						
							| 34 | 5 | fveq2d | ⊢ ( 𝜑  →  ( ♯ ‘ 𝑆 )  =  ( ♯ ‘ ( ( 𝐴  ++  𝐵 )  ++  𝐶 ) ) ) | 
						
							| 35 | 6 | oveq1d | ⊢ ( 𝜑  →  ( 𝐹  +  ( ♯ ‘ 𝐵 ) )  =  ( ( ♯ ‘ 𝐴 )  +  ( ♯ ‘ 𝐵 ) ) ) | 
						
							| 36 |  | ccatlen | ⊢ ( ( 𝐴  ∈  Word  𝑋  ∧  𝐵  ∈  Word  𝑋 )  →  ( ♯ ‘ ( 𝐴  ++  𝐵 ) )  =  ( ( ♯ ‘ 𝐴 )  +  ( ♯ ‘ 𝐵 ) ) ) | 
						
							| 37 | 1 2 36 | syl2anc | ⊢ ( 𝜑  →  ( ♯ ‘ ( 𝐴  ++  𝐵 ) )  =  ( ( ♯ ‘ 𝐴 )  +  ( ♯ ‘ 𝐵 ) ) ) | 
						
							| 38 | 35 7 37 | 3eqtr4d | ⊢ ( 𝜑  →  𝑇  =  ( ♯ ‘ ( 𝐴  ++  𝐵 ) ) ) | 
						
							| 39 | 38 | oveq1d | ⊢ ( 𝜑  →  ( 𝑇  +  ( ♯ ‘ 𝐶 ) )  =  ( ( ♯ ‘ ( 𝐴  ++  𝐵 ) )  +  ( ♯ ‘ 𝐶 ) ) ) | 
						
							| 40 | 33 34 39 | 3eqtr4d | ⊢ ( 𝜑  →  ( ♯ ‘ 𝑆 )  =  ( 𝑇  +  ( ♯ ‘ 𝐶 ) ) ) | 
						
							| 41 | 19 | nn0zd | ⊢ ( 𝜑  →  𝑇  ∈  ℤ ) | 
						
							| 42 | 41 | uzidd | ⊢ ( 𝜑  →  𝑇  ∈  ( ℤ≥ ‘ 𝑇 ) ) | 
						
							| 43 |  | lencl | ⊢ ( 𝐶  ∈  Word  𝑋  →  ( ♯ ‘ 𝐶 )  ∈  ℕ0 ) | 
						
							| 44 | 3 43 | syl | ⊢ ( 𝜑  →  ( ♯ ‘ 𝐶 )  ∈  ℕ0 ) | 
						
							| 45 |  | uzaddcl | ⊢ ( ( 𝑇  ∈  ( ℤ≥ ‘ 𝑇 )  ∧  ( ♯ ‘ 𝐶 )  ∈  ℕ0 )  →  ( 𝑇  +  ( ♯ ‘ 𝐶 ) )  ∈  ( ℤ≥ ‘ 𝑇 ) ) | 
						
							| 46 | 42 44 45 | syl2anc | ⊢ ( 𝜑  →  ( 𝑇  +  ( ♯ ‘ 𝐶 ) )  ∈  ( ℤ≥ ‘ 𝑇 ) ) | 
						
							| 47 | 40 46 | eqeltrd | ⊢ ( 𝜑  →  ( ♯ ‘ 𝑆 )  ∈  ( ℤ≥ ‘ 𝑇 ) ) | 
						
							| 48 |  | elfzuzb | ⊢ ( 𝑇  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) )  ↔  ( 𝑇  ∈  ( ℤ≥ ‘ 0 )  ∧  ( ♯ ‘ 𝑆 )  ∈  ( ℤ≥ ‘ 𝑇 ) ) ) | 
						
							| 49 | 31 47 48 | sylanbrc | ⊢ ( 𝜑  →  𝑇  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 50 |  | ccatpfx | ⊢ ( ( 𝑆  ∈  Word  𝑋  ∧  𝐹  ∈  ( 0 ... 𝑇 )  ∧  𝑇  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) )  →  ( ( 𝑆  prefix  𝐹 )  ++  ( 𝑆  substr  〈 𝐹 ,  𝑇 〉 ) )  =  ( 𝑆  prefix  𝑇 ) ) | 
						
							| 51 | 12 30 49 50 | syl3anc | ⊢ ( 𝜑  →  ( ( 𝑆  prefix  𝐹 )  ++  ( 𝑆  substr  〈 𝐹 ,  𝑇 〉 ) )  =  ( 𝑆  prefix  𝑇 ) ) | 
						
							| 52 |  | lencl | ⊢ ( 𝑆  ∈  Word  𝑋  →  ( ♯ ‘ 𝑆 )  ∈  ℕ0 ) | 
						
							| 53 | 12 52 | syl | ⊢ ( 𝜑  →  ( ♯ ‘ 𝑆 )  ∈  ℕ0 ) | 
						
							| 54 | 53 22 | eleqtrdi | ⊢ ( 𝜑  →  ( ♯ ‘ 𝑆 )  ∈  ( ℤ≥ ‘ 0 ) ) | 
						
							| 55 |  | eluzfz2 | ⊢ ( ( ♯ ‘ 𝑆 )  ∈  ( ℤ≥ ‘ 0 )  →  ( ♯ ‘ 𝑆 )  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 56 | 54 55 | syl | ⊢ ( 𝜑  →  ( ♯ ‘ 𝑆 )  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 57 |  | ccatpfx | ⊢ ( ( 𝑆  ∈  Word  𝑋  ∧  𝑇  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) )  ∧  ( ♯ ‘ 𝑆 )  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) )  →  ( ( 𝑆  prefix  𝑇 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) )  =  ( 𝑆  prefix  ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 58 | 12 49 56 57 | syl3anc | ⊢ ( 𝜑  →  ( ( 𝑆  prefix  𝑇 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) )  =  ( 𝑆  prefix  ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 59 |  | pfxid | ⊢ ( 𝑆  ∈  Word  𝑋  →  ( 𝑆  prefix  ( ♯ ‘ 𝑆 ) )  =  𝑆 ) | 
						
							| 60 | 12 59 | syl | ⊢ ( 𝜑  →  ( 𝑆  prefix  ( ♯ ‘ 𝑆 ) )  =  𝑆 ) | 
						
							| 61 | 58 60 5 | 3eqtrd | ⊢ ( 𝜑  →  ( ( 𝑆  prefix  𝑇 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) )  =  ( ( 𝐴  ++  𝐵 )  ++  𝐶 ) ) | 
						
							| 62 |  | pfxcl | ⊢ ( 𝑆  ∈  Word  𝑋  →  ( 𝑆  prefix  𝑇 )  ∈  Word  𝑋 ) | 
						
							| 63 | 12 62 | syl | ⊢ ( 𝜑  →  ( 𝑆  prefix  𝑇 )  ∈  Word  𝑋 ) | 
						
							| 64 |  | swrdcl | ⊢ ( 𝑆  ∈  Word  𝑋  →  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 )  ∈  Word  𝑋 ) | 
						
							| 65 | 12 64 | syl | ⊢ ( 𝜑  →  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 )  ∈  Word  𝑋 ) | 
						
							| 66 |  | pfxlen | ⊢ ( ( 𝑆  ∈  Word  𝑋  ∧  𝑇  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) )  →  ( ♯ ‘ ( 𝑆  prefix  𝑇 ) )  =  𝑇 ) | 
						
							| 67 | 12 49 66 | syl2anc | ⊢ ( 𝜑  →  ( ♯ ‘ ( 𝑆  prefix  𝑇 ) )  =  𝑇 ) | 
						
							| 68 | 67 38 | eqtrd | ⊢ ( 𝜑  →  ( ♯ ‘ ( 𝑆  prefix  𝑇 ) )  =  ( ♯ ‘ ( 𝐴  ++  𝐵 ) ) ) | 
						
							| 69 |  | ccatopth | ⊢ ( ( ( ( 𝑆  prefix  𝑇 )  ∈  Word  𝑋  ∧  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 )  ∈  Word  𝑋 )  ∧  ( ( 𝐴  ++  𝐵 )  ∈  Word  𝑋  ∧  𝐶  ∈  Word  𝑋 )  ∧  ( ♯ ‘ ( 𝑆  prefix  𝑇 ) )  =  ( ♯ ‘ ( 𝐴  ++  𝐵 ) ) )  →  ( ( ( 𝑆  prefix  𝑇 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) )  =  ( ( 𝐴  ++  𝐵 )  ++  𝐶 )  ↔  ( ( 𝑆  prefix  𝑇 )  =  ( 𝐴  ++  𝐵 )  ∧  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 )  =  𝐶 ) ) ) | 
						
							| 70 | 63 65 9 3 68 69 | syl221anc | ⊢ ( 𝜑  →  ( ( ( 𝑆  prefix  𝑇 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) )  =  ( ( 𝐴  ++  𝐵 )  ++  𝐶 )  ↔  ( ( 𝑆  prefix  𝑇 )  =  ( 𝐴  ++  𝐵 )  ∧  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 )  =  𝐶 ) ) ) | 
						
							| 71 | 61 70 | mpbid | ⊢ ( 𝜑  →  ( ( 𝑆  prefix  𝑇 )  =  ( 𝐴  ++  𝐵 )  ∧  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 )  =  𝐶 ) ) | 
						
							| 72 | 71 | simpld | ⊢ ( 𝜑  →  ( 𝑆  prefix  𝑇 )  =  ( 𝐴  ++  𝐵 ) ) | 
						
							| 73 | 51 72 | eqtrd | ⊢ ( 𝜑  →  ( ( 𝑆  prefix  𝐹 )  ++  ( 𝑆  substr  〈 𝐹 ,  𝑇 〉 ) )  =  ( 𝐴  ++  𝐵 ) ) | 
						
							| 74 |  | pfxcl | ⊢ ( 𝑆  ∈  Word  𝑋  →  ( 𝑆  prefix  𝐹 )  ∈  Word  𝑋 ) | 
						
							| 75 | 12 74 | syl | ⊢ ( 𝜑  →  ( 𝑆  prefix  𝐹 )  ∈  Word  𝑋 ) | 
						
							| 76 |  | swrdcl | ⊢ ( 𝑆  ∈  Word  𝑋  →  ( 𝑆  substr  〈 𝐹 ,  𝑇 〉 )  ∈  Word  𝑋 ) | 
						
							| 77 | 12 76 | syl | ⊢ ( 𝜑  →  ( 𝑆  substr  〈 𝐹 ,  𝑇 〉 )  ∈  Word  𝑋 ) | 
						
							| 78 |  | uztrn | ⊢ ( ( ( ♯ ‘ 𝑆 )  ∈  ( ℤ≥ ‘ 𝑇 )  ∧  𝑇  ∈  ( ℤ≥ ‘ 𝐹 ) )  →  ( ♯ ‘ 𝑆 )  ∈  ( ℤ≥ ‘ 𝐹 ) ) | 
						
							| 79 | 47 28 78 | syl2anc | ⊢ ( 𝜑  →  ( ♯ ‘ 𝑆 )  ∈  ( ℤ≥ ‘ 𝐹 ) ) | 
						
							| 80 |  | elfzuzb | ⊢ ( 𝐹  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) )  ↔  ( 𝐹  ∈  ( ℤ≥ ‘ 0 )  ∧  ( ♯ ‘ 𝑆 )  ∈  ( ℤ≥ ‘ 𝐹 ) ) ) | 
						
							| 81 | 23 79 80 | sylanbrc | ⊢ ( 𝜑  →  𝐹  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) ) | 
						
							| 82 |  | pfxlen | ⊢ ( ( 𝑆  ∈  Word  𝑋  ∧  𝐹  ∈  ( 0 ... ( ♯ ‘ 𝑆 ) ) )  →  ( ♯ ‘ ( 𝑆  prefix  𝐹 ) )  =  𝐹 ) | 
						
							| 83 | 12 81 82 | syl2anc | ⊢ ( 𝜑  →  ( ♯ ‘ ( 𝑆  prefix  𝐹 ) )  =  𝐹 ) | 
						
							| 84 | 83 6 | eqtrd | ⊢ ( 𝜑  →  ( ♯ ‘ ( 𝑆  prefix  𝐹 ) )  =  ( ♯ ‘ 𝐴 ) ) | 
						
							| 85 |  | ccatopth | ⊢ ( ( ( ( 𝑆  prefix  𝐹 )  ∈  Word  𝑋  ∧  ( 𝑆  substr  〈 𝐹 ,  𝑇 〉 )  ∈  Word  𝑋 )  ∧  ( 𝐴  ∈  Word  𝑋  ∧  𝐵  ∈  Word  𝑋 )  ∧  ( ♯ ‘ ( 𝑆  prefix  𝐹 ) )  =  ( ♯ ‘ 𝐴 ) )  →  ( ( ( 𝑆  prefix  𝐹 )  ++  ( 𝑆  substr  〈 𝐹 ,  𝑇 〉 ) )  =  ( 𝐴  ++  𝐵 )  ↔  ( ( 𝑆  prefix  𝐹 )  =  𝐴  ∧  ( 𝑆  substr  〈 𝐹 ,  𝑇 〉 )  =  𝐵 ) ) ) | 
						
							| 86 | 75 77 1 2 84 85 | syl221anc | ⊢ ( 𝜑  →  ( ( ( 𝑆  prefix  𝐹 )  ++  ( 𝑆  substr  〈 𝐹 ,  𝑇 〉 ) )  =  ( 𝐴  ++  𝐵 )  ↔  ( ( 𝑆  prefix  𝐹 )  =  𝐴  ∧  ( 𝑆  substr  〈 𝐹 ,  𝑇 〉 )  =  𝐵 ) ) ) | 
						
							| 87 | 73 86 | mpbid | ⊢ ( 𝜑  →  ( ( 𝑆  prefix  𝐹 )  =  𝐴  ∧  ( 𝑆  substr  〈 𝐹 ,  𝑇 〉 )  =  𝐵 ) ) | 
						
							| 88 | 87 | simpld | ⊢ ( 𝜑  →  ( 𝑆  prefix  𝐹 )  =  𝐴 ) | 
						
							| 89 | 88 | oveq1d | ⊢ ( 𝜑  →  ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  =  ( 𝐴  ++  𝑅 ) ) | 
						
							| 90 | 71 | simprd | ⊢ ( 𝜑  →  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 )  =  𝐶 ) | 
						
							| 91 | 89 90 | oveq12d | ⊢ ( 𝜑  →  ( ( ( 𝑆  prefix  𝐹 )  ++  𝑅 )  ++  ( 𝑆  substr  〈 𝑇 ,  ( ♯ ‘ 𝑆 ) 〉 ) )  =  ( ( 𝐴  ++  𝑅 )  ++  𝐶 ) ) | 
						
							| 92 | 21 91 | eqtrd | ⊢ ( 𝜑  →  ( 𝑆  splice  〈 𝐹 ,  𝑇 ,  𝑅 〉 )  =  ( ( 𝐴  ++  𝑅 )  ++  𝐶 ) ) |