DB<3> p $a
olivia-niels-peter-lars-niels-lars-olivia-olivia
  DB<4> @hash{ split '-',$a } = ()

  DB<5> x keys %hash
0  'lars'
1  'niels'
2  'peter'
3  'olivia'
  DB<6> p join '-', keys %hash
lars-niels-peter-olivia
  DB<7>