New in version 2.0.
Flatten sequence at indices:
abjad> from abjad.tools import sequencetools
abjad> sequencetools.flatten_sequence_at_indices([0, 1, [2, 3, 4], [5, 6, 7]], [3])
[0, 1, [2, 3, 4], 5, 6, 7]
Flatten sequence at negative indices:
abjad> sequencetools.flatten_sequence_at_indices([0, 1, [2, 3, 4], [5, 6, 7]], [-1])
[0, 1, [2, 3, 4], 5, 6, 7]
Leave sequence unchanged.
Return newly constructed sequence object.