assertNoMatch = sets => {
    const [[label1, set1], [label2, set2]] = Object.entries(sets);
    t.is(
      matches(set1, set2),
      false,
      `${label1} specimen must not be matched by ${label2} pattern`,
    );
    t.is(
      matches(set2, set1),
      false,
      `${label2} specimen must not be matched by ${label1} pattern`,
    );
  }
@param {Key[]} arr an array of unique Key values
@param {Iterator<boolean>} keepSeq a sequence of booleans for filtering
  arr into a subset