Description: Two ways of expressing "exactly one" element. (Contributed by Zhi Wang, 23-Sep-2024)
Ref | Expression | ||
---|---|---|---|
Assertion | reutru | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | tru | |
|
2 | 1 | biantru | |
3 | 2 | eubii | |
4 | df-reu | |
|
5 | 3 4 | bitr4i | |