Description: A symbol in a prefix of a word, indexed using the prefix' indices. (Contributed by Alexander van der Vekens, 16-Jun-2018) (Revised by AV, 3-May-2020)
Ref | Expression | ||
---|---|---|---|
Assertion | pfxfv | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | elfznn0 | |
|
2 | pfxval | |
|
3 | 1 2 | sylan2 | |
4 | 3 | 3adant3 | |
5 | 4 | fveq1d | |
6 | simp1 | |
|
7 | 0elfz | |
|
8 | 1 7 | syl | |
9 | 8 | 3ad2ant2 | |
10 | simp2 | |
|
11 | 1 | nn0cnd | |
12 | 11 | subid1d | |
13 | 12 | eqcomd | |
14 | 13 | oveq2d | |
15 | 14 | eleq2d | |
16 | 15 | biimpd | |
17 | 16 | a1i | |
18 | 17 | 3imp | |
19 | swrdfv | |
|
20 | 6 9 10 18 19 | syl31anc | |
21 | elfzoelz | |
|
22 | 21 | zcnd | |
23 | 22 | addridd | |
24 | 23 | 3ad2ant3 | |
25 | 24 | fveq2d | |
26 | 5 20 25 | 3eqtrd | |