NameError: name 'chord' is not defined in 07_01_notation_compose.ipynb

[emres]

NameError: name 'chord' is not defined in 07_01_notation_compose.ipynb:

NameError                                 Traceback (most recent call last)
<ipython-input-5-fbeff2cc0330> in <module>
      4 for element in original_score.flat:
      5 
----> 6     if isinstance(element, chord.Chord):
      7         notes.append('.'.join(n.nameWithOctave for n in element.pitches))
      8         durations.append(element.duration.quarterLength)

NameError: name 'chord' is not defined

because chord is missing from the imports. There's a similar problem with note:

from music21 import converter