The honest can't say :"I am a liar" , because he can't lie. The liar can't say :"I am a liar", because he can't say the truth. When someone in this boolean universe (where each person can be honest XOR liar) uses the words "All people are liars" he is included too. It means that no one in this boolean universe can say those words, Therefore, there is no paradox. What do you think ?