In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

[Q]: What needs consistency?, Context: The simplest valve gears give events of fixed length during the engine cycle and often make the engine rotate in only one direction. Most however have a reversing mechanism which additionally can provide means for saving steam as speed and momentum are gained by gradually "shortening the cutoff" or rather, shortening the admission event; this in turn proportionately lengthens the expansion period. However, as one and the same valve usually controls both steam flows, a short cutoff at admission adversely affects the exhaust and compression periods which should ideally always be kept fairly constant; if the exhaust event is too brief, the totality of the exhaust steam cannot evacuate the cylinder, choking it and giving excessive compression ("kick back").[citation needed]
[A]: exhaust and compression periods


[Q]: Who has studied the Mahayana?, Context: There is no evidence that Mahāyāna ever referred to a separate formal school or sect of Buddhism, but rather that it existed as a certain set of ideals, and later doctrines, for bodhisattvas. Initially it was known as Bodhisattvayāna (the "Vehicle of the Bodhisattvas"). Paul Williams has also noted that the Mahāyāna never had nor ever attempted to have a separate Vinaya or ordination lineage from the early schools of Buddhism, and therefore each bhikṣu or bhikṣuṇī adhering to the Mahāyāna formally belonged to an early school. This continues today with the Dharmaguptaka ordination lineage in East Asia, and the Mūlasarvāstivāda ordination lineage in Tibetan Buddhism. Therefore Mahāyāna was never a separate rival sect of the early schools. From Chinese monks visiting India, we now know that both Mahāyāna and non-Mahāyāna monks in India often lived in the same monasteries side by side.
[A]: Paul Williams


[Q]: How did the theory change?, Context: Hayek's principal investigations in economics concerned capital, money, and the business cycle. Mises had earlier applied the concept of marginal utility to the value of money in his Theory of Money and Credit (1912), in which he also proposed an explanation for "industrial fluctuations" based on the ideas of the old British Currency School and of Swedish economist Knut Wicksell. Hayek used this body of work as a starting point for his own interpretation of the business cycle, elaborating what later became known as the "Austrian Theory of the Business Cycle". Hayek spelled out the Austrian approach in more detail in his book, published in 1929, an English translation of which appeared in 1933 as Monetary Theory and the Trade Cycle. There he argued for a monetary approach to the origins of the cycle. In his Prices and Production (1931), Hayek argued that the business cycle resulted from the central bank's inflationary credit expansion and its transmission over time, leading to a capital misallocation caused by the artificially low interest rates. Hayek claimed that "the past instability of the market economy is the consequence of the exclusion of the most important regulator of the market mechanism, money, from itself being regulated by the market process".
[A]:
he also proposed an explanation for "industrial fluctuations" based on the ideas of the old British Currency School