| Step | Hyp | Ref | Expression | 
						
							| 1 |  | seqseq123d.1 |  | 
						
							| 2 |  | seqseq123d.2 |  | 
						
							| 3 |  | seqseq123d.3 |  | 
						
							| 4 | 2 | oveqd |  | 
						
							| 5 | 3 | fveq1d |  | 
						
							| 6 | 5 | oveq2d |  | 
						
							| 7 | 4 6 | eqtrd |  | 
						
							| 8 | 7 | opeq2d |  | 
						
							| 9 | 8 | mpoeq3dv |  | 
						
							| 10 | 3 1 | fveq12d |  | 
						
							| 11 | 1 10 | opeq12d |  | 
						
							| 12 |  | rdgeq12 |  | 
						
							| 13 | 9 11 12 | syl2anc |  | 
						
							| 14 | 13 | imaeq1d |  | 
						
							| 15 |  | df-seqs |  | 
						
							| 16 |  | df-seqs |  | 
						
							| 17 | 14 15 16 | 3eqtr4g |  |