That's why I said its not so clear.
However the trick should work because:
1) One decides whether he chooses to be a truth-teller or a liar before answering the question.
2) When evaluating/reading the question they know they are and forever will be either a truth-teller or a liar. This way, they are forced to answer to any question regarding the future, since they now their allegiance now (truth-teller, liar).
1 cannot be false since otherwise they cannot answer the first question as a truth-teller or a liar. They need to look and interpret the question.
2 cannot be false since it follows logically from 1 and the OP "And as he did he will be fixed to that persona and will not change it( i.e.If he tells the truth,will always tell the truth, if he lied,will always lie)"
Wolfgang, I understand you tried to create a random outcome of the first question but it's just not possible in the context of this OP.
They cannot at the same time be random for the first question AND decide to be truth-teller or liar for all eternity.
They need to look at the question and interpret/evaluate it before answering. There's no way to come up with a YES/NO answer without looking at the question.
- what if they choose No and the question is "Are you going to tell the truth forever?". Contradiction since both truth-teller and liars answer Yes to that question.
- what if they choose Yes and the question is "Are you going to lie forever?". Contradiction since both truth-teller and liars answer No to that question.
So, you cannot choose the answer randomly without looking at the question and afterwards claiming either to be a truth-teller or a liar (depending on the answer). You break consistency that way. They need to decide before answering and need to look and interpret the question.