theorem Th34:
  Ex(x,H) = Ex(y,G) implies x = y & H = G
proof
  assume Ex(x,H) = Ex(y,G);
  then
A1: All(x,'not' H) = All(y,'not' G) by FINSEQ_1:33;
  then 'not' H = 'not' G by Th3;
  hence thesis by A1,Th3,FINSEQ_1:33;
end;
