>>> from graf_exp import *

>>> 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)
>>> lve = vars_expr(g, 'b+c')
>>> print (sorted(lve))
['b', 'c']
>>> lve = vars_expr(g, 'a*(b+c)')
>>> print (sorted(lve))
['a', 'b', 'c']
>>> lve = vars_expr(g, 'a*(b+c)-c/b')
>>> print (sorted(lve))
['a', 'b', 'c']