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Along the same lines, '''[[co-NP]]''' is the class containing the [[Complement (complexity)|complement]] problems (i.e. problems with the ''yes''/''no'' answers reversed) of '''NP''' problems. It is believed<ref>[http://www.cs.princeton.edu/courses/archive/spr06/cos522/ Boaz Barak's course on Computational Complexity] [http://www.cs.princeton.edu/courses/archive/spr06/cos522/lec2.pdf Lecture 2]</ref> that '''NP''' is not equal to '''co-NP'''; however, it has not yet been proven. It is clear that if these two complexity classes are not equal then '''P''' is not equal to '''NP''', since '''P'''='''co-P'''.  Thus if '''P'''='''NP''' we would have '''co-P'''='''co-NP''' whence '''NP'''='''P'''='''co-P'''='''co-NP'''.  

Along the same lines, '''[[co-NP]]''' is the class containing the [[Complement (complexity)|complement]] problems (i.e. problems with the ''yes''/''no'' answers reversed) of '''NP''' problems. It is believed<ref>[http://www.cs.princeton.edu/courses/archive/spr06/cos522/ Boaz Barak's course on Computational Complexity] [http://www.cs.princeton.edu/courses/archive/spr06/cos522/lec2.pdf Lecture 2]</ref> that '''NP''' is not equal to '''co-NP'''; however, it has not yet been proven. It is clear that if these two complexity classes are not equal then '''P''' is not equal to '''NP''', since '''P'''='''co-P'''.  Thus if '''P'''='''NP''' we would have '''co-P'''='''co-NP''' whence '''NP'''='''P'''='''co-P'''='''co-NP'''.  

“是的，问题的答案与‘NP’的问题是相反的。据信<ref>[http://www.cs.princeton.edu/courses/archive/spr06/cos522/博阿斯·巴拉克关于计算复杂性的课程][http://www.cs.princeton.edu/courses/archive/spr06/cos522/lec2.pdf“NP”不等于“co-NP”，但它还没有被证明。很明显，如果这两个复杂度类不相等，那么“P”就不等于“NP”，因为“P”=“co-P”。因此，如果''P''=''NP''，我们将有''co-P'''=''co-NP''，其中''NP'''=''P''=''co-P'''=''co-NP''。

“是的，问题的答案与‘NP’的问题是相反的。据信<ref>[http://www.cs.princeton.edu/courses/archive/spr06/cos522/ Boaz Barak's course on Computational Complexity] [http://www.cs.princeton.edu/courses/archive/spr06/cos522/lec2.pdf Lecture 2]</ref> “NP”不等于“co-NP”，但它还没有被证明。很明显，如果这两个复杂度类不相等，那么“P”就不等于“NP”，因为“P”=“co-P”。因此，如果''P''=''NP''，我们将有''co-P'''=''co-NP''，其中''NP'''=''P''=''co-P'''=''co-NP''。

Similarly, it is not known if '''L''' (the set of all problems that can be solved in logarithmic space) is strictly contained in '''P''' or equal to '''P'''. Again, there are many complexity classes between the two, such as '''NL''' and '''NC''', and it is not known if they are distinct or equal classes.

Similarly, it is not known if '''L''' (the set of all problems that can be solved in logarithmic space) is strictly contained in '''P''' or equal to '''P'''. Again, there are many complexity classes between the two, such as '''NL''' and '''NC''', and it is not known if they are distinct or equal classes.