 reserve X, Y for set, A for Ordinal;
 reserve z,z1,z2 for Complex;
 reserve r,r1,r2 for Real;
 reserve q,q1,q2 for Rational;
 reserve i,i1,i2 for Integer;
 reserve n,n1,n2 for Nat;

theorem
  modRel(4) = {[0,1], [1,2], [2,3], [3,0]}
proof
  thus modRel(4) = succRel(4) \/ {[4-1,0]} by Th41
    .= {[0,1], [1,2], [2,3], [3,0]} by Th8, ENUMSET1:6;
end;
