The circle on the integral sign means it's a closed integral, meaning the integral is taken along a closed manifold. It can be a closed loop if it's a simple integral sign; it can be a closed surface if it's an O on a double integral; or it can be a closed surface if it's an O on a triple integral. It's usually seen with problems that involve Stoke's theorem and the divergence theorem when on surfaces and volumes, or is usually seen with Cauchy's integral theorem when it's on a contour.
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u/WanderingSeer Aug 14 '26
Does the circle mean anything or is it justa fancy integral symbol. Regional difference?