Description: If x is not free in ph , ps , and ch , it is not free in ( ph /\ ps /\ ch ) . (Contributed by NM, 14-Sep-2003) (Proof shortened by Wolf Lammen, 2-Jan-2018)
Ref | Expression | ||
---|---|---|---|
Hypotheses | hb.1 | |
|
hb.2 | |
||
hb.3 | |
||
Assertion | hb3an | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | hb.1 | |
|
2 | hb.2 | |
|
3 | hb.3 | |
|
4 | 1 | nf5i | |
5 | 2 | nf5i | |
6 | 3 | nf5i | |
7 | 4 5 6 | nf3an | |
8 | 7 | nf5ri | |