reserve x,y,z, X,Y,Z for set,
  n for Element of NAT;
reserve A for set,
  D for non empty set,
  a,b,c,l,r for Element of D,
  o,o9 for BinOp of D,
  f,g,h for Function of A,D;
reserve G for non empty multMagma;
reserve A for non empty set,
  a for Element of A,
  p for FinSequence of A,
  m1,m2 for Multiset of A;

theorem
  |.<*> A.|.a = 0
proof
  dom ({a}|`{}) c= dom {} by FUNCT_1:56;
  then dom ({a}|`<*> A) = {};
  hence thesis by Def7,CARD_1:27;
end;
