^ #seq

    ^ self acceptsEpsilonOpenSet: IdentitySet new.

    set add: self.

    ^ self children allSatisfy: [:e | e acceptsEpsilonOpenSet: set ]

    (aSet includes: self) ifTrue: [ ^ aCollection ].

    aSet add: self.

    (block value: self) ifTrue: [ aCollection add: self. ^ aCollection ].

    self children do: [ :child | 

        child firstSetSuchThat: block into: aCollection openSet: aSet.

        child acceptsEpsilon ifFalse: [ ^ aCollection ]

    ].

    ^ aCollection

    | nullable |

    "TODO JK: aBlock is ignored by now"

    children do: [ :node |

        nullable := false.

        (aFirstDictionary at: node) do: [ :each |

            each isNullable

                ifTrue: [ nullable := true ]

                ifFalse: [ aSet add: each ] ].

        nullable

            ifFalse: [ ^ self ] ].

    aSet add: PPCSentinelNode instance

!

recognizedSentencesPrim

    | retval |

    (self children anySatisfy: [ :child | child hasFiniteLanguage not ]) ifTrue: [ ^ #() ].

    retval := Set with: ''.

    self children do: [ : child |

        | set |

        set := Set new.

        child recognizedSentences do: [ :suffix |

            retval do: [ :prefix |

                set add: prefix, suffix.

         	]

        ].

        retval := set.

    ].

    ^ retval asArray

    |  guard firsts |

    (compiler guards not or: [(guard := PPCGuard on: self) makesSense not]) ifTrue: [ ^ self].

    firsts := (self firstSetSuchThat: [ :e | (e isKindOf: PPCTrimmingTokenNode) or: [ e isTerminal ] ]).

    (firsts allSatisfy: [ :e | e isKindOf: PPCTrimmingTokenNode ]) ifTrue: [  

        "If we start with trimming, we should invoke the whitespace parser"

        firsts anyOne compileWhitespace: compiler.

        compiler add: 'context atEnd ifTrue: [ ^ self error ].'.

        guard id: id, '_guard'.

        guard compileGuard: compiler.

        compiler addOnLine: 'ifFalse: [ ^ self error ].'

    ].

    (firsts allSatisfy: [ :e | e isTerminal ]) ifTrue: [  

        compiler add: 'context atEnd ifTrue: [ ^ self error ].'.

        guard id: id, '_guard'.

        guard compileGuard: compiler.

        compiler addOnLine: 'ifFalse: [ ^ self error ].'

    ].

    children keysAndValuesDo: [ :index :node |

        | follow first |

        follow := aFollowDictionary at: node.

        index = children size

            ifTrue: [ follow addAll: aSet ]

            ifFalse: [

                (self class withAll: (children 

                    copyFrom: index + 1 to: children size))

                        firstSets: aFirstDictionary

                        into: (first := IdentitySet new)

                        suchThat: aBlock.

                (first anySatisfy: [ :each | each isNullable ])

                    ifTrue: [ follow addAll: aSet ].

                follow addAll: (first 

                    reject: [ :each | each isNullable ]) ] ]

    ^ visitor visitSequenceNode: self