Sequential　circuit　is　a　common　logic　device　whose　output　values,　at　a　given　instant,　depend　upon　its　input　values　and　the　internal　state　at　that　instant,　and　whose　internal　state　depends　upon　the(66)preceding　input　values　and　the　preceding　internal　state.　A　sequential　circuit　can　assume　a　finite　number　of　internal　states　and　may　therefore　be　regarded,　from　an　abstract(67),　as　a　finite(68).Combinational　circuit　is　another　logic　device　whose　output　values,　at　any　given　instant,　depend　upon　the　input　values　at　that　instant.　A　combinational　circuit　is　a(69)of　a　sequential　circuit　whose　internal　state　is　not　taken(70).

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Artificial　intelligence (AI) ,an　interdisciplinary　field,　is　usually　regarded　as　a　branch　of　computer　science,　dealing　with　models　and　systems　for　the　performance　of　functions　generally　associated　with　human　intelligence,　such　as(71)and　learning.In　AI,　knowledge-based　system　is　an　information(72)system　that　provides　for　solving　problems　in　a　particular　domain　or　application　area　by　drawing　inferences　from　a　knowledge　base.　Moreover,　some　knowledge-based　systems　have　learning　capabilities.　Expert　system (ES) indicates　the　knowledge-based　system　that　provides　for　solving　problems　in　a　particular　domain　or　application　area　by　drawing　inferences　from　a　knowledge　base　developed　from　human(73).　Some　expert　systems　are　able　to(74)their　knowledge　base　and　develop　new　inference　rules　based　on　their　experience　with　previous　problems.　The　term　"expert　system"　is　sometimes　used(75)with　"knowledge-based　system",　but　should　be　taken　to　emphasize　expert　knowledge.

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