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* Test each S-prime component to see if it is an interval graph.
:This can be done by truly building the
'''Lemma'''
Let u<sub>k</sub> be the next interval to be placed, which is not a neighbor of previously chosen intervals. Let u<sub>j</sub> be the parent of u<sub>k</sub> and u<sub>i</sub> be the parent of u<sub>j</sub> in the BFS-tree. It can be determined uniquely which endpoints of u<sub>j</sub> or u<sub>i</sub> is contained in u<sub>k</sub>.
There are three cases, place each edge according to its category.
Case 1: (f(u<sub>i</sub>), u<sub>j</sub>) ∉ E. If u<sub>i</sub> ,u<sub>k</sub> are on the different side of u<sub>j</sub>, u<sub>k</sub> would contain u<sub>j</sub>.
Case 2: (f(u<sub>k</sub>), u<sub>j</sub> ) ∉ E. Again, if u<sub>i</sub>, u<sub>k</sub> are on the different side of u<sub>j</sub>, u<sub>k</sub> would contain u<sub>j</sub>.
Case 3: (f(u<sub>j</sub>), u<sub>k</sub>) ∉ E and (f(u<sub>j</sub>), u<sub>i</sub>) ∉ E. If u<sub>i</sub> ,u<sub>k</sub> are on the different sides of u<sub>j</sub>, u<sub>k</sub> cannot be adjacent to u<sub>i</sub>.
::(''f''(''u'') := ''u'''s neighbor vertex with the smallest ''π''-index.)
==Related families of graphs==
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