Note that adjacency matrix can also be conceived as a directed graph (DAG). ret[i,j] iff i <= j
rel_graph(x, pord, ...)list with elements to compare, preferrably named
function with 2 arguments, returning boolean value
additional arguments passed to pord
square 0-1 Matrix (of class Matrix)
Other binary_relations: closure_total_fair;
closure_transitive;
de_transitive;
get_equivalence_classes;
get_incomparable_pairs;
get_independent_sets;
is_reflexive; is_total;
is_transitive; pord_weakdom