Metamath Proof Explorer
Description: A variable not free in a wff remains so in a restricted iota descriptor.
(Contributed by NM, 12-Oct-2011)
|
|
Ref |
Expression |
|
Hypotheses |
nfriota.1 |
|
|
|
nfriota.2 |
|
|
Assertion |
nfriota |
|
Proof
Step |
Hyp |
Ref |
Expression |
1 |
|
nfriota.1 |
|
2 |
|
nfriota.2 |
|
3 |
|
nftru |
|
4 |
1
|
a1i |
|
5 |
2
|
a1i |
|
6 |
3 4 5
|
nfriotadw |
|
7 |
6
|
mptru |
|