Suppose my brother is telling the truth, then today must be Thursday, because if it is any day before Thursday, he will lie again today. If it was Wednesday, then yesterday was Tuesday. He did lie yesterday, but he also lied today, which is inconsistent with the hypothesis, so it can't be Monday, Tuesday and Wednesday. By analogy, today will not be the day after Friday or Sunday.
Suppose my brother told the truth and lied in April, May and June, then suppose today is Monday and yesterday is Sunday, and he lied, which contradicts the topic; It doesn't matter that today is Tuesday and yesterday is Monday; The possibility of Wednesday can also be ruled out. If today is Thursday, then he should lie today. He said that he lied yesterday, which is true and in line with the problem. Suppose today is Friday, but he should have lied, but he told the truth. From I lied yesterday, I know there is no Friday, Saturday and Sunday. To sum up, both conclusions are Thursday, so today is Thursday.
I hope my answer can help you.
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