Yes and no. The point is this: You start with a set of premises P, to which you apply a set of logical deductions D(P). The logical and computational machinery in D can be flawless but still yield the wrong answer, since it depends on the correctness of the input P. If P is rubbish, then D(P) is rubbish, even if D itself is flawless. No matter how formally correct your deductions or computations are, if the input is incorrect, your results are also incorrect. This is semi-formally known as garbage in, garbage out. Or more vulgarly as shit in, shit out.
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