reserve i,j,m,n,k for Nat,
  x,y for set,
  K for Field,
  a,a1,a2 for Element of K,
  D for non empty set,
  d,d1,d2 for Element of D,
  M,M1,M2 for (Matrix of D),
  A,A1,A2,B1,B2 for (Matrix of K),
  f,g for FinSequence of NAT;

theorem Th12:
  {} is FinSequence_of_Matrix of D
proof
  set F=<*>(D**);
  for i st i in dom F holds F.i is Matrix of D;
  hence thesis by Def2;
end;
