>>> from graf_exp import crea_digraf_camins

>>> lc = [
... ['a*(b+c)-c/b', 'a*(b+c)', 'a'],
... ['a*(b+c)-c/b', 'c/b', 'b'],
... ['a*(b+c)', 'b+c'],
... ['b+c', 'b'],
... ['b+c', 'c'],
... ['c/b', 'c']]
>>> g = crea_digraf_camins(lc)
>>> sorted(g.nodes())
['a', 'a*(b+c)', 'a*(b+c)-c/b', 'b', 'b+c', 'c', 'c/b']
>>> for i, e in enumerate(sorted(g.edges())):
...   print(e)
('a*(b+c)', 'a')
('a*(b+c)', 'b+c')
('a*(b+c)-c/b', 'a*(b+c)')
('a*(b+c)-c/b', 'c/b')
('b+c', 'b')
('b+c', 'c')
('c/b', 'b')
('c/b', 'c')