#problem  a question raised for consideration or solution; "our homework consisted of ten problems to solve"
  supertype:  #question.subject__head  the subject matter at issue; "the question of disease merits serious discussion"; "under the head of minor Roman poets"
  subtype:  #puzzler__puzzle__mystifier  a particularly baffling problem that is said to have a correct solution; "he loved to solve chessmate puzzles"; "that's a real puzzler"
  subtype:  #case.problem  a problem requiring investigation; "Perry Mason solved the case of the missing heir"
  subtype:  #homework_problem  a problem that students are assigned to do outside of class
  subtype:  #conundrum__riddle__enigma__brain-teaser__brainteaser  a difficult problem
  subtype:  #stumper__toughie__sticker  a particularly difficult or baffling question or problem
  subtype:  #Gordian_knot.problem__gordianknot  any very difficult problem; insoluble in its own terms
  subtype:  #crossword_puzzle__crosswordpuzzle  a puzzle in which words corresponding to numbered clues are to be found and written in to squares in the puzzle
  subtype:  #word_square__acrostic  a puzzle where you fill a square grid with words reading the same down as across
  subtype:  #pons_asinorum  a problem that severely tests the ability of an inexperienced person
  subtype:  #rebus__rebu  a puzzle where you decode a message consisting of pictures representing syllables and words

No statement uses or specializes #problem; click here to add one.