reserve X for BCI-algebra;
reserve x,y,z,u,a,b for Element of X;
reserve IT for non empty Subset of X;

theorem Th22:
  X is SubAlgebra of X
proof
  dom(the InternalDiff of X) = [:the carrier of X,the carrier of X:] by
FUNCT_2:def 1;
  then
  0.X = 0.X & the InternalDiff of X =(the InternalDiff of X)||the carrier
  of X;
  hence thesis by Def10;
end;
