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returns an arbitrary point on l. It holds point(i) == point(j), iff i==j. Furthermore, is directed from point(i) to point(j), for all i j. | ||
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returns a point on r. point(0) is the source,
point(i), with , is different from the
source. Precondition: . | ||
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returns source or target of s: point(0) returns the source of s, point(1) returns the target of s. The parameter i is taken modulo 2, which gives easy access to the other end point. |