>>> from filter_sts2 import filter_sts2

>>> L = [[778, ['B', 'A-', 'C-']], [223, ['B-', 'B+', 'A']], [112, ['B', 'A', 'C+']], [445, ['D', 'C-', 'C']]]

>>> filter_sts2(L, 'C')    # doctesttag: +TAG=1_filter_sts2
[[112, ['B', 'A', 'C+']], [223, ['B-', 'B+', 'A']], [445, ['C']], [778, ['B', 'A-']]]

>>> filter_sts2(L, 'B')    # doctesttag: +TAG=1_filter_sts2
[[112, ['B', 'A']], [223, ['B+', 'A']], [778, ['B', 'A-']]]

>>> filter_sts2(L, 'B+')    # doctesttag: +TAG=1_filter_sts2
[[112, ['A']], [223, ['B+', 'A']], [778, ['A-']]]

>>> filter_sts2(L, 'A+')    # doctesttag: +TAG=1_filter_sts2
[]