| Step | Hyp | Ref | Expression | 
						
							| 1 |  | decma.a | ⊢ 𝐴  ∈  ℕ0 | 
						
							| 2 |  | decma.b | ⊢ 𝐵  ∈  ℕ0 | 
						
							| 3 |  | decma.c | ⊢ 𝐶  ∈  ℕ0 | 
						
							| 4 |  | decma.d | ⊢ 𝐷  ∈  ℕ0 | 
						
							| 5 |  | decma.m | ⊢ 𝑀  =  ; 𝐴 𝐵 | 
						
							| 6 |  | decma.n | ⊢ 𝑁  =  ; 𝐶 𝐷 | 
						
							| 7 |  | decaddc.e | ⊢ ( ( 𝐴  +  𝐶 )  +  1 )  =  𝐸 | 
						
							| 8 |  | decaddc.f | ⊢ 𝐹  ∈  ℕ0 | 
						
							| 9 |  | decaddc.2 | ⊢ ( 𝐵  +  𝐷 )  =  ; 1 𝐹 | 
						
							| 10 |  | 10nn0 | ⊢ ; 1 0  ∈  ℕ0 | 
						
							| 11 |  | dfdec10 | ⊢ ; 𝐴 𝐵  =  ( ( ; 1 0  ·  𝐴 )  +  𝐵 ) | 
						
							| 12 | 5 11 | eqtri | ⊢ 𝑀  =  ( ( ; 1 0  ·  𝐴 )  +  𝐵 ) | 
						
							| 13 |  | dfdec10 | ⊢ ; 𝐶 𝐷  =  ( ( ; 1 0  ·  𝐶 )  +  𝐷 ) | 
						
							| 14 | 6 13 | eqtri | ⊢ 𝑁  =  ( ( ; 1 0  ·  𝐶 )  +  𝐷 ) | 
						
							| 15 |  | dfdec10 | ⊢ ; 1 𝐹  =  ( ( ; 1 0  ·  1 )  +  𝐹 ) | 
						
							| 16 | 9 15 | eqtri | ⊢ ( 𝐵  +  𝐷 )  =  ( ( ; 1 0  ·  1 )  +  𝐹 ) | 
						
							| 17 | 10 1 2 3 4 12 14 8 7 16 | numaddc | ⊢ ( 𝑀  +  𝑁 )  =  ( ( ; 1 0  ·  𝐸 )  +  𝐹 ) | 
						
							| 18 |  | dfdec10 | ⊢ ; 𝐸 𝐹  =  ( ( ; 1 0  ·  𝐸 )  +  𝐹 ) | 
						
							| 19 | 17 18 | eqtr4i | ⊢ ( 𝑀  +  𝑁 )  =  ; 𝐸 𝐹 |