If two functions have the same divergence and curl in some region, then are they equal?

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If two functions have the same divergence and curl in some region, then are the functions equal?

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Then their difference will have the same divergence and curl. So you are asking whether a vector field of zero divergence and curl is necessarily zero.

There a trivial counterexamples to this; for instance a constant vector field.

There are less trivial examples too. If $f$ is a harmonic function, its gradient has divergence zero (essentially the definition of harmonic function) while every gradient has curl zero. So you can take the gradient of a harmonic function. There are lots of harmonic functions...