my %hash=(
  'MEX1J' => { 
    desc => 'Job 2' ,
    pred => ['TEX1J'],
  },
  'MEX2J' => { 
    desc => 'Job end',
    pred => ['TROUBLE'], 
   },
  'TEX1J' => { 
    desc => 'Job start',
    pred => [], 
   },
  'TROUBLE' => {
    desc => 'who cares',
    pred => ['MEX1J']
  }
);