Context: Distributed systems

I am not sure I understand Byzantine agreement problem(BAP) completely. Clearly BAP is not possible to solve when we have 3 processes (P_1,..,P_3) of which 1 is byzantine. Suppose then we try to solve BAP for a system where say 6 processes (P_1,...,P_6) and are Byzantine. Can we prove that this also cannot be solved, and how do we prove that in that case given the previous assertion?

Thanks

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