A B-flat major Giovanni Battista Pergolesi piece in this genre is the only non-choral work featured on Claudio Abbado's landmark Pergolesi Collection. A composer wrote the words "Easy to enter; difficult to escape!" in the score of another work in this genre nicknamed the "Harmonic Labyrinth" by Pietro Locatelli. A collection of these works by a different composer cycles through the number of solo parts to be either four, two, or one. A viola plays a two-note "always forte" motif in one of these pieces by a composer who included 12 of them in "The Harmonic Inspiration." (-5[1])That composer included "For Pisendel" and "The Storm at Sea" in another collection of works in this genre, which contains four of them accompanied by sonnets. For 10 points, name this genre of Vivaldi's The Contest Between Harmony and Invention, including "The Four Seasons." ■END■ (10[1])