The way to determine whether or not an argument is valid, then, is really to ignore the actual truth-values of the premises and the actual truth-value of the conclusion (of course, if you know that the conclusion is actually false, yet the premises are all true, then the argument must be invalid. But normally when assessing arguments we do not know the truth-value of the conclusion, because the whole reason for considering the argument is that we want to find out the truth-value of the conclusion). The way to do it - and this is what the definition of validity should lead you to expect - is to reason as follows:

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