Two distinct point pairs 
and 
separate each other if 
, 
, 
, and 
lie on a circle (or line) in such
order that either of the arcs (or the line segment 
)
contains one but not both of 
and 
. In addition, the point pairs
separate each other if every circle through 
and 
intersects (or coincides with) every circle
through 
and 
. If the point pairs separate each other, then the symbol
is used.
Separation
See also
Separation of Variables, Separation TheoremExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Separation." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Separation.html