docs: function get_trit(n,i) {
    // convert entire number to balanced ternary string then slice
    // would be nice to extract without converting everything, see extract_digit(), which
    // works for unbalanced ternary, but balanced converts 2 -> 1i, so individual digit extraction
    // is more difficult -- see https://en.wikipedia.org/wiki/Balanced_ternary#Conversion_from_ternary
    var s = n2bts(n);
    return ~~BT_DIGIT_TO_N[s.charAt(s.length - i - 1)];
  }