; Recursive
@var rec &[a v l h] [
  @if < h l @return null
  @var m @/ +h l 2
  @? {
    > `m a v @!rec[a v l -m 1]
    < `m a v @!rec[a v +1 m h]
    m
  }
]

; Iterative
@var itr &[a v] [
  @vars{l 0 h #-a}
  @while <= l h [
    @var m @/ +l h 2
    @iff {
      > `m a v :h -m 1
      < `m a v :l +m 1
      @return m
    }
  ]
  null
]