anchor.diff:      ;
   
   sequence_source
  -    :logical_stateful_source|sequence_collection_stateful_source|standard_stateful_source
  +    :logical_stateful_source|sequence_collection_stateful_source|standard_stateful_source|logical_absent_stateful_source
       ;
   
   sequence_collection_stateful_source
  
positive.code:     ;
  
  pattern_stream
      :every_pattern_source_chain
      ;
  
  every_pattern_source_chain
  
negative.code:     | pattern_source within_time?
      ;
  
  absent_pattern_source_chain
      : EVERY? '('absent_pattern_source_chain')' within_time?
      | every_absent_pattern_source
      | left_absent_pattern_source
      | right_absent_pattern_source
      ;
  
  left_absent_pattern_source
      : EVERY? '('left_absent_pattern_source')' within_time?
      | every_absent_pattern_source '->' every_pattern_source_chain
      | left_absent_pattern_source '->' left_absent_pattern_source
      | left_absent_pattern_source '->' every_absent_pattern_source
      | every_pattern_source_chain '->' left_absent_pattern_source
      ;
  
  right_absent_pattern_source
      : EVERY? '('right_absent_pattern_source')' within_time?
      | every_pattern_source_chain '->' every_absent_pattern_source
      | right_absent_pattern_source '->' right_absent_pattern_source
      | every_absent_pattern_source '->' right_absent_pattern_source
      | right_absent_pattern_source '->' every_pattern_source_chain
      ;
  
  pattern_source
      :logical_stateful_source|pattern_collection_stateful_source|standard_stateful_source|logical_absent_stateful_source
      ;
  
  logical_stateful_source
      :standard_stateful_source AND standard_stateful_source
      |standard_stateful_source OR standard_stateful_source
      ;
  
  logical_absent_stateful_source
      : '(' logical_absent_stateful_source ')'
      | standard_stateful_source AND NOT basic_source
      | NOT basic_source AND standard_stateful_source
      | standard_stateful_source AND basic_absent_pattern_source
      | basic_absent_pattern_source AND standard_stateful_source
      | basic_absent_pattern_source AND basic_absent_pattern_source
      | standard_stateful_source OR basic_absent_pattern_source
      | basic_absent_pattern_source OR standard_stateful_source
      | basic_absent_pattern_source OR basic_absent_pattern_source
      ;
  
  every_absent_pattern_source
      : EVERY? basic_absent_pattern_source
      ;
  
  basic_absent_pattern_source
      : NOT basic_source for_time
      ;
  
  pattern_collection_stateful_source
  