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<p>of other expressions can be used because the metric tensor can raise and lower the components of  or . For contra/co-variant components of  and co/contra-variant components of , we have:</p>

<p>so in the matrix notation:</p>

<p>while for  and  each in covariant components:</p>

<p>with a similar matrix expression to the above.</p>

<p>Applying the Minkowski tensor to a four-vector  with itself we get:</p>

<p>which, depending on the case, may be considered the square, or its negative, of the length of the vector.</p>

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