    "Given a stream of tuples, return two streams. The
     first stream produces the first elements of the
     given tuples, and the second stream produces the
     remaining elements of the given tuples.

     Thus:

         unzip(tuples)[i]==[tuples[i].first,*tuples[i].rest]"
    shared [{Head*}, {Tail*}] unzip<Element,Head,Tail>
            ({Tuple<Element|Head,Head,Tail>*} tuples)
            given Tail satisfies Element[]
            => [tuples.map((Tuple<Element|Head,Head,Tail> tuple) => tuple.first),
                tuples.map((Tuple<Element|Head,Head,Tail> tuple) => tuple.rest)];

    "Given a stream of pairs, return two streams. The
     first stream produces the first elements of the
     given pairs, and the second stream produces the
     second elements of the given pairs.

     Thus:

         unzipPairs(pairs)[i]==[pairs[i][0],pairs[i][1]]"
    shared [{First*}, {Second*}] unzipPairs<First,Second>
            ({[First,Second]*} pairs)
            => [pairs.map(([First,Second] pair) => pair[0]),
                pairs.map(([First,Second] pair) => pair[1])];

    "Given a stream of entries, return two streams. The
     first stream produces the keys of the given entries,
     and the second stream produces the items of the given
     entries.

     Thus:

         unzipEntries(entries)[i]==[entries[i].key,entries[i].item]"
    shared [{Key*}, {Item*}] unzipEntries<Key,Item>
            ({<Key->Item>*} entries)
            given Key satisfies Object
            given Item satisfies Object
            => [entries.map(Entry<Key,Item>.key),
                entries.map(Entry<Key,Item>.item)];