If each musician is holding two instruments.
return musicians ;return instruments ;return #2 that #1 are  holding ;return number of #3 for each #1 ;return #1 where #4 is  equal to two ;return number of #1 ;return number of #5 ;return if  #7 is  equal to #6
['select', 'select', 'filter', 'group', 'comparative', 'aggregate', 'aggregate', 'boolean']