* Jonathan L Gross, Jay Yellen, ''Graph Theory and its applications'', second edition, 2006 (p 97, Incidence Matrices for undirected graphs; p 98, incidence matrices for digraphs) | * Jonathan L Gross, Jay Yellen, ''Graph Theory and its applications'', second edition, 2006 (p 97, Incidence Matrices for undirected graphs; p 98, incidence matrices for digraphs) |