Function vstd::seq_lib::lemma_seq_skip_update_commut1

source ·

pub proof fn lemma_seq_skip_update_commut1<A>(s: Seq<A>, i: int, v: A, n: int)

Expand description

ensures

0 <= n <= i < s.len()
    ==> #[trigger] s.update(i, v).skip(n) =~= s.skip(n).update(i - n, v),

If i is a valid index after the first n indices of sequence s, updating sequence s at index i with value v and then skipping the first n elements is equivalent to skipping the first n elements of s and then updating index i-n to value v.