theorem Th92:
  {a},{b} are_conjugated iff a,b are_conjugated
proof
  thus {a},{b} are_conjugated implies a,b are_conjugated
  proof
    assume {a},{b} are_conjugated;
    then consider g such that
A1: {a} * g = {b} by Th88;
    {b} = {a * g} by A1,ThB37;
    hence thesis by Th74,ZFMISC_1:3;
  end;
  assume a,b are_conjugated;
  then consider g such that
A2: a * g = b by Th74;
  {b} = {a} * g by A2,ThB37;
  hence thesis by Th88;
end;
