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 Web Resource. https://mathworld.wolfram.com/Separation.html