let G be Group; :: thesis: for g being Element of G holds {g} " = {(g ")}
let g be Element of G; :: thesis: {g} " = {(g ")}
thus {g} " c= {(g ")} :: according to XBOOLE_0:def 10 :: thesis: {(g ")} c= {g} "

proof

let x be object ; :: according to TARSKI:def 3 :: thesis: ( not x in {g} " or x in {(g ")} )
assume x in {g} " ; :: thesis: x in {(g ")}
then consider h being Element of G such that
A1: x = h " and
A2: h in {g} ;
h = g by A2, TARSKI:def 1;
hence x in {(g ")} by A1, TARSKI:def 1; :: thesis: verum

end;

let x be object ; :: according to TARSKI:def 3 :: thesis: ( not x in {(g ")} or x in {g} " )
assume x in {(g ")} ; :: thesis: x in {g} "
then A3: x = g " by TARSKI:def 1;
g in {g} by TARSKI:def 1;
hence x in {g} " by A3; :: thesis: verum