# binary search

Binary search

x'y

**Binary search** performs a binary search for `y`

in a list `x`

, assuming `x`

is sorted in ascending order. It returns the smallest index `i`

such that `y`

would sort after (or matches) `x[i]`

, or -1 if no such index exists.

binary search is right atomic.

0 2 4 6 8 10'5 2 0 2 4 6 8 10'-10 0 4 5 6 20 -1 0 2 2 3 5