| Step | Hyp | Ref | Expression | 
						
							| 1 |  | istrkg.p |  | 
						
							| 2 |  | istrkg.d |  | 
						
							| 3 |  | istrkg.i |  | 
						
							| 4 |  | simpl |  | 
						
							| 5 | 4 | difeq1d |  | 
						
							| 6 |  | simpr |  | 
						
							| 7 | 6 | oveqd |  | 
						
							| 8 | 7 | eleq2d |  | 
						
							| 9 | 6 | oveqd |  | 
						
							| 10 | 9 | eleq2d |  | 
						
							| 11 | 6 | oveqd |  | 
						
							| 12 | 11 | eleq2d |  | 
						
							| 13 | 8 10 12 | 3orbi123d |  | 
						
							| 14 | 4 13 | rabeqbidv |  | 
						
							| 15 | 4 5 14 | mpoeq123dv |  | 
						
							| 16 | 15 | eqeq2d |  | 
						
							| 17 | 1 3 16 | sbcie2s |  | 
						
							| 18 |  | fveqeq2 |  | 
						
							| 19 | 17 18 | bitrd |  | 
						
							| 20 |  | eqid |  | 
						
							| 21 | 19 20 | elab4g |  |