Given that we have a statement $Q$ that has some probability.
How can we show that if you initially believe that $Q$ has probability 1, this belief should never change? That is, show that if $P_{old}(Q)=1$, then given any evidence $P$, $P_{new}(Q)=1$.
I've been heavily stuck on this problem and don't know how to explicitly show it without using basic logic. Also, depending on what we define $Q$ as, won't there be at least one new possible piece of evidence that WILL, in fact, change the probability of $Q$?