QuotientGraph( gamma, R )
Let S be the smallest gamma.group-invariant equivalence relation on the vertices of gamma, such that S contains the relation R (which should be a list of ordered pairs (length 2 lists) of vertices of gamma). Then this function returns a graph isomorphic to the quotient delta of the graph gamma, defined as follows. The vertices of delta are the equivalence classes of S, and [X,Y] is an edge of delta if and only if [x,y] is an edge of gamma for some x in X, y in Y.
gap> gamma := JohnsonGraph(4,2);; gap> QuotientGraph( gamma, [[1,6]] ); rec( isGraph := true, order := 3, group := Group( (1,2), (1,3), (2,3) ), schreierVector := [ -1, 1, 2 ], adjacencies := [ [ 2, 3 ] ], representatives := [ 1 ], isSimple := true, names := [ [ [ 1, 2 ], [ 3, 4 ] ], [ [ 1, 3 ], [ 2, 4 ] ], [ [ 1, 4 ], [ 2, 3 ] ] ] )
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