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A MultiCurve is a one-dimensional geometry.

A MultiCurve is simple if and only if all of its elements are simple; the only intersections between any two elements occur at points that are on the boundaries of both elements.

A MultiCurve boundary is obtained by applying the 「mod 2 union rule」 (also known as the 「odd-even rule」): A point is in the boundary of a MultiCurve if it is in the boundaries of an odd number of MultiCurve elements.

A MultiCurve is closed if all of its elements are closed.

The boundary of a closed MultiCurve is always empty.