 reserve x for Real,
    p,k,l,m,n,s,h,i,j,k1,t,t1 for Nat,
    X for Subset of REAL;
reserve x for object, X,Y,Z for set;
 reserve M,N for Cardinal;
reserve X for non empty set,
  s for sequence of X;

theorem
  s^\k^\m = s^\m^\k
proof
  thus s^\k^\m = s^\(k+m) by Th35
    .= s^\m^\k by Th35;
end;
