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[itex]\oint\oint\frac{d\vec{l_{1}}\cdot d\vec{l_{2}}}{r}[/itex],

where [itex]r[/itex] is the distance between the length elements [itex]\vec{dl_{1}}[/itex] and [itex]\vec{dl_{2}}[/itex].

Is this integral always positive? If so, what would be the mathematical treatment associated to prove its positivity?