question: @ Nullable private static Boolean findPath ( Instruction cur , int destination , LinkedHashSet < Integer > fragmentInsns , boolean wasOutside , HashMap < Instruction , Boolean > visited ) { wasOutside = wasOutside || ! fragmentInsns . contains ( cur . num ( ) ) ; visited . put ( cur , null ) ; Iterable < ? extends Instruction > instructions = cur . allSuccessors ( ) ; boolean pathExists = false ; for ( Instruction i : instructions ) { if ( i . num ( ) == destination ) return wasOutside ; Boolean result ; if ( visited . containsKey ( i ) ) { result = visited . get ( i ) ; } else { result = findPath ( i , destination , fragmentInsns , wasOutside , visited ) ; visited . put ( i , result ) ; } if ( result != null ) { if ( result . booleanValue ( ) ) { visited . put ( cur , true ) ; return true ; } pathExists = true ; } } if ( pathExists ) { visited . put ( cur , false ) ; return false ; } else { visited . put ( cur , null ) ; return null ; } }
target:  return true if path is outside of fragment, null if there is no pathand false if path is inside fragment