A metric on a bunch of segments with a common endpoint 
, which defines the distance between
two points 
and 
as the length of the shortest path connecting them inside this geometric configuration.
If 
and 
lie on the same segment, this is the length of segment 
. Otherwise, it is the sum of the lengths of segment 
and segment 
.
Hedgehog Metric
See also
Hedgehog, MetricThis entry contributed by Margherita Barile
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References
Willard, S. General Topology. Reading, MA: Addison-Wesley, p. 16, 1970.Referenced on Wolfram|Alpha
Hedgehog MetricCite this as:
Barile, Margherita. "Hedgehog Metric." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/HedgehogMetric.html