| Step | Hyp | Ref | Expression | 
						
							| 1 |  | swrdccatin2.l | ⊢ 𝐿  =  ( ♯ ‘ 𝐴 ) | 
						
							| 2 |  | ccatcl | ⊢ ( ( 𝐴  ∈  Word  𝑉  ∧  𝐵  ∈  Word  𝑉 )  →  ( 𝐴  ++  𝐵 )  ∈  Word  𝑉 ) | 
						
							| 3 | 2 | adantr | ⊢ ( ( ( 𝐴  ∈  Word  𝑉  ∧  𝐵  ∈  Word  𝑉 )  ∧  ( 𝑀  ∈  ( 0 ... 𝐿 )  ∧  𝑁  ∈  ( 𝐿 ... ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) ) ) )  →  ( 𝐴  ++  𝐵 )  ∈  Word  𝑉 ) | 
						
							| 4 |  | elfz0fzfz0 | ⊢ ( ( 𝑀  ∈  ( 0 ... 𝐿 )  ∧  𝑁  ∈  ( 𝐿 ... ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) ) )  →  𝑀  ∈  ( 0 ... 𝑁 ) ) | 
						
							| 5 | 4 | adantl | ⊢ ( ( ( 𝐴  ∈  Word  𝑉  ∧  𝐵  ∈  Word  𝑉 )  ∧  ( 𝑀  ∈  ( 0 ... 𝐿 )  ∧  𝑁  ∈  ( 𝐿 ... ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) ) ) )  →  𝑀  ∈  ( 0 ... 𝑁 ) ) | 
						
							| 6 |  | elfzuz2 | ⊢ ( 𝑀  ∈  ( 0 ... 𝐿 )  →  𝐿  ∈  ( ℤ≥ ‘ 0 ) ) | 
						
							| 7 |  | fzss1 | ⊢ ( 𝐿  ∈  ( ℤ≥ ‘ 0 )  →  ( 𝐿 ... ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) )  ⊆  ( 0 ... ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) ) ) | 
						
							| 8 | 6 7 | syl | ⊢ ( 𝑀  ∈  ( 0 ... 𝐿 )  →  ( 𝐿 ... ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) )  ⊆  ( 0 ... ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) ) ) | 
						
							| 9 | 8 | sselda | ⊢ ( ( 𝑀  ∈  ( 0 ... 𝐿 )  ∧  𝑁  ∈  ( 𝐿 ... ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) ) )  →  𝑁  ∈  ( 0 ... ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) ) ) | 
						
							| 10 |  | ccatlen | ⊢ ( ( 𝐴  ∈  Word  𝑉  ∧  𝐵  ∈  Word  𝑉 )  →  ( ♯ ‘ ( 𝐴  ++  𝐵 ) )  =  ( ( ♯ ‘ 𝐴 )  +  ( ♯ ‘ 𝐵 ) ) ) | 
						
							| 11 | 1 | oveq1i | ⊢ ( 𝐿  +  ( ♯ ‘ 𝐵 ) )  =  ( ( ♯ ‘ 𝐴 )  +  ( ♯ ‘ 𝐵 ) ) | 
						
							| 12 | 10 11 | eqtr4di | ⊢ ( ( 𝐴  ∈  Word  𝑉  ∧  𝐵  ∈  Word  𝑉 )  →  ( ♯ ‘ ( 𝐴  ++  𝐵 ) )  =  ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) ) | 
						
							| 13 | 12 | oveq2d | ⊢ ( ( 𝐴  ∈  Word  𝑉  ∧  𝐵  ∈  Word  𝑉 )  →  ( 0 ... ( ♯ ‘ ( 𝐴  ++  𝐵 ) ) )  =  ( 0 ... ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) ) ) | 
						
							| 14 | 13 | eleq2d | ⊢ ( ( 𝐴  ∈  Word  𝑉  ∧  𝐵  ∈  Word  𝑉 )  →  ( 𝑁  ∈  ( 0 ... ( ♯ ‘ ( 𝐴  ++  𝐵 ) ) )  ↔  𝑁  ∈  ( 0 ... ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) ) ) ) | 
						
							| 15 | 9 14 | imbitrrid | ⊢ ( ( 𝐴  ∈  Word  𝑉  ∧  𝐵  ∈  Word  𝑉 )  →  ( ( 𝑀  ∈  ( 0 ... 𝐿 )  ∧  𝑁  ∈  ( 𝐿 ... ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) ) )  →  𝑁  ∈  ( 0 ... ( ♯ ‘ ( 𝐴  ++  𝐵 ) ) ) ) ) | 
						
							| 16 | 15 | imp | ⊢ ( ( ( 𝐴  ∈  Word  𝑉  ∧  𝐵  ∈  Word  𝑉 )  ∧  ( 𝑀  ∈  ( 0 ... 𝐿 )  ∧  𝑁  ∈  ( 𝐿 ... ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) ) ) )  →  𝑁  ∈  ( 0 ... ( ♯ ‘ ( 𝐴  ++  𝐵 ) ) ) ) | 
						
							| 17 | 3 5 16 | 3jca | ⊢ ( ( ( 𝐴  ∈  Word  𝑉  ∧  𝐵  ∈  Word  𝑉 )  ∧  ( 𝑀  ∈  ( 0 ... 𝐿 )  ∧  𝑁  ∈  ( 𝐿 ... ( 𝐿  +  ( ♯ ‘ 𝐵 ) ) ) ) )  →  ( ( 𝐴  ++  𝐵 )  ∈  Word  𝑉  ∧  𝑀  ∈  ( 0 ... 𝑁 )  ∧  𝑁  ∈  ( 0 ... ( ♯ ‘ ( 𝐴  ++  𝐵 ) ) ) ) ) |