theorem
  for f, g being Assign of BASSModel(R,BASSIGN) holds SIGMA(f) = SIGMA(g)
  implies f=g
proof
  let f,g be Assign of BASSModel(R,BASSIGN);
  assume
A1: SIGMA(f) = SIGMA(g);
  SIGMA(f) = { s where s is Element of S : (Fid(f,S)).s=TRUE } by Lm40;
  then { s where s is Element of S : (Fid(f,S)).s=TRUE } = { s where s is
  Element of S : (Fid(g,S)).s=TRUE } by A1,Lm40;
  hence thesis by Lm41,Lm42;
end;
