The Schrijver graph 
is the induced subgraph of the Kneser
graph on the 
-element
subsets of 
containing no two consecutive elements in the cyclic
order 
,
where 
and 
.
Two vertices are adjacent iff
their corresponding subsets are disjoint
(Bondy and Murty 2008, p. 369).
In particular, a permitted subset cannot contain both 1 and 
.
The notation here follows Bondy and Murty (2008), with 
denoting the subset size and 
the size of the underlying set.
Schrijver (1978) proved that the chromatic number is 
and that each subgraph obtained by vertex
deletion has chromatic number 
. Thus 
is a vertex-critical
graph with the same chromatic number as its
ambient Kneser graph. For example, 
has chromatic number
4, whereas deleting any graph vertex leaves a graph of chromatic number
3 (Bondy and Murty 2008, p. 369).
