Metamath Proof Explorer


Theorem pfxfv

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 WWordVL0WI0..^LWprefixLI=WI

Proof

Step Hyp Ref Expression
1 elfznn0 L0WL0
2 pfxval WWordVL0WprefixL=Wsubstr0L
3 1 2 sylan2 WWordVL0WWprefixL=Wsubstr0L
4 3 3adant3 WWordVL0WI0..^LWprefixL=Wsubstr0L
5 4 fveq1d WWordVL0WI0..^LWprefixLI=Wsubstr0LI
6 simp1 WWordVL0WI0..^LWWordV
7 0elfz L000L
8 1 7 syl L0W00L
9 8 3ad2ant2 WWordVL0WI0..^L00L
10 simp2 WWordVL0WI0..^LL0W
11 1 nn0cnd L0WL
12 11 subid1d L0WL0=L
13 12 eqcomd L0WL=L0
14 13 oveq2d L0W0..^L=0..^L0
15 14 eleq2d L0WI0..^LI0..^L0
16 15 biimpd L0WI0..^LI0..^L0
17 16 a1i WWordVL0WI0..^LI0..^L0
18 17 3imp WWordVL0WI0..^LI0..^L0
19 swrdfv WWordV00LL0WI0..^L0Wsubstr0LI=WI+0
20 6 9 10 18 19 syl31anc WWordVL0WI0..^LWsubstr0LI=WI+0
21 elfzoelz I0..^LI
22 21 zcnd I0..^LI
23 22 addridd I0..^LI+0=I
24 23 3ad2ant3 WWordVL0WI0..^LI+0=I
25 24 fveq2d WWordVL0WI0..^LWI+0=WI
26 5 20 25 3eqtrd WWordVL0WI0..^LWprefixLI=WI