piece = segment of sequences, i.e., an aggregate of simultaneous voicesExample: { [ c1*1/4 c1*1/4 ], [ e1*1/4 f1*1/4 ], [ g1*1/4 a1*1/4 ] }
piece = sequence of segments, i.e., a succession of chordsExample: [ {c1*1/4, e1*1/4, g1*1/4} {c1*1/4, f1*1/4, a1*1/4} ]
{ ..., [ ... { ... , ... } ... ], ... }