The Four Cycles (skor bzhi), which comprise the Experiential Precept Series (man ngag gi sde), are: 1) the External Cycle, 2) the Internal Cycle, 3) the Secret Cycle, and 4) the Unsurpassed Secret Cycle, also known as the Seminal Heart (snying thig). Each of the four self-consciously claims superiority over its predecessors. The lower three cycles (skor gsum) represent the development of movements culminating in the fourth over a period from the latter half of the 10th century to the first half of the 12th century. Vimalamitra is the dominant 8th-century Indian patron of these texts.