 reserve I for non empty set;
 reserve i for Element of I;
 reserve F for Group-Family of I;
 reserve G for Group;
reserve S for Subgroup-Family of F;
reserve f for Homomorphism-Family of G, F;

theorem :: missing
  for G1,G2,G3 being Group
  for f1 being Homomorphism of G1,G2
  for f2 being Homomorphism of G2,G3
  for g being Element of G1
  holds (f2 * f1).g = f2.(f1.g)
proof
  let G1,G2,G3 be Group;
  let f1 be Homomorphism of G1,G2;
  let f2 be Homomorphism of G2,G3;
  let g be Element of G1;
  dom f1 = the carrier of G1 by FUNCT_2:def 1;
  hence (f2 * f1).g = f2.(f1.g) by FUNCT_1:13;
end;
