Description: Threefold conjunction inside and outside of a substitution are equivalent. (Contributed by NM, 14-Dec-2006)
Ref | Expression | ||
---|---|---|---|
Assertion | sb3an |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-3an | ||
2 | 1 | sbbii | |
3 | sban | ||
4 | sban | ||
5 | 4 | anbi1i | |
6 | df-3an | ||
7 | 5 6 | bitr4i | |
8 | 2 3 7 | 3bitri |