Description: Define the base set (also called underlying set, ground set, carrier set, or carrier) extractor for extensible structures. (Contributed by NM, 4-Sep-2011) (Revised by Mario Carneiro, 14-Aug-2015)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | df-base | |- Base = Slot 1 |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 0 | cbs | |- Base |
|
| 1 | c1 | |- 1 |
|
| 2 | 1 | cslot | |- Slot 1 |
| 3 | 0 2 | wceq | |- Base = Slot 1 |