{ 1 , 2 , 3 }                  # == {1,2,3}
{ 1 , 2 , 3 , 2 , 1}           # == {1,2,3}
{1,2} inter {1,3}              # == {1}
({1,2} union {1,3}) inter {3,4,5}  # == {3}
 {1,2} union {1,3}  inter {3,4,5}  # == {1,2,3}
{0,1,2,3,4,5} diff {1,3,5}     # == {0,2,4}
S_2 = {1,2,4,8,16,32,64,128}   # == ca depend des bornes
S_2                            #
S_2 inter comp S_2             # == {} quelque soit S_2
comp S_2 union S_2             # == All elem
S_3 = S_2                      #
{1} union {1,2} union {}       # =={1,2}
{1,}                  # Error
S_111                 # Error
S_2 comp S_3          # Error
{1}                   # verif resynchro apres erreur == {1}