The structure of a musical piece with its 3 parts and its thematic elements. The structure of a musical piece divided into three parts and two thematic elements. The shape or structure of the second part "Andante" from the Mozart Concerto in A major K488, includes three parts. The part A presents the first theme, itself divided into two elements: a1 and a2. The exposure of the first theme is followed by a transition or "bridge", which brings the second part B including the second theme. The theme B is itself concluded by a transition that brings back the part A, a recapitulation that we will call A', because slightly modified. The section A' can be considered as a real restatement of the theme A with its two elements a1 and a2, followed by a commentary of the second thematic element a that we call a'2, a kind of ornamental variation of the a2 element, played at the piano. Then we have a short transition that leads us to the coda or conclusion of this piece.