reserve S for non empty non void ManySortedSign;
reserve X for non-empty ManySortedSet of S;
reserve x,y,z for set, i,j for Nat;

theorem Th21:
  for I being set
  for A being ManySortedSet of I
  for B being non-empty ManySortedSet of I holds
  A is_transformable_to B
  proof
    let I be set;
    let A be ManySortedSet of I;
    let B be non-empty ManySortedSet of I;
     for i being set st i in I holds B.i = {} implies A.i = {};
    hence A is_transformable_to B by PZFMISC1:def 3;
  end;
