reserve X for BCI-algebra;
reserve n for Nat;
reserve x,y for Element of X;
reserve a,b for Element of AtomSet(X);
reserve m,n for Nat;
reserve i,j for Integer;

theorem
  (a |^ (-1))|^ (-1) = a
proof
  (a |^ -1)|^ -1 = (a`)|^ -1 by Th5
    .= a`` by Th5;
  hence thesis by BCIALG_1:29;
end;
