The Johnson graph
is defined as the graph whose vertices are the
-subsets of
the set
,
where two vertices are adjacent if they share exactly
elements. Unlike Johnson graphs, induced subgraphs of Johnson graphs
(JIS for short) do not seem to have been studied before. We give some
necessary conditions and some sufficient conditions for a graph to be JIS,
including: in a JIS graph, any two maximal cliques share at most two
vertices; all trees, cycles, and complete graphs are JIS; disjoint unions
and Cartesian products of JIS graphs are JIS; every JIS graph of order
is an induced
subgraph of
for some
.
This last result gives an algorithm for deciding if a graph is JIS. We also show that
all JIS graphs are edge move distance graphs, but not vice versa.