The Greeks analyzed genera using various terms, including diatonic, enharmonic, and chromatic. Similarly, some notes of the chromatic scale have enharmonic equivalents in solfege. It is similar to enharmonic equivalence, octave equivalence, and inversional equivalence. It is similar to enharmonic equivalency, octave equivalency and even transpositional equivalency. There are two main types of enharmonic modulations&colon; dominant seventh/augmented sixth, and (fully) diminished seventh. The chromatic scale has no set enharmonic spelling that is always used. A two-bar bridge achieves this transition with Franck's characteristic combination of enharmonic and chromatic modulation. The concept of interval class accounts for octave, enharmonic, and inversional equivalency. A 12-tone scale is obtained by removing one note for each couple of enharmonic notes. The theme and its accompanying chords are written using strikingly eccentric and impractical enharmonic notation. These keys are easily interchanged using enharmonic equivalents. In other tuning systems, such enharmonic equivalences in general do not exist. Other types of enharmonic modulation include the augmented triad (III+) and French sixth (Fr+). Its enharmonic equivalents are C and A. Its direct enharmonic equivalent, F-sharp major, contains the same number of sharps; .