Description: The number 9 is a complex number. (Contributed by David A. Wheeler, 8-Dec-2018) Reduce dependencies on axioms. (Revised by Steven Nguyen, 4-Oct-2022)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | 9cn | |- 9 e. CC |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | df-9 | |- 9 = ( 8 + 1 ) |
|
| 2 | 8cn | |- 8 e. CC |
|
| 3 | ax-1cn | |- 1 e. CC |
|
| 4 | 2 3 | addcli | |- ( 8 + 1 ) e. CC |
| 5 | 1 4 | eqeltri | |- 9 e. CC |