// functions: L<F1>
// functions are columns, elements are rows
static L<L> map_multi(Collection functions, Iterable c) {
  new L<L> out;
  fOr (O a : c) {
    new L row;
    fOr (O f : functions)
      row.add(callF(f, a));
    out.add(row);
  }
  ret out;
}