A sequence of LLs and LHs is called downtrend. A decline from Relative High to Relative Low is called a major phase (impulse). A rally from Relative Low to Relative High is called a corrective phase (reaction, pullback, recovery). Major phase + corrective phase form full cycle. In other words a cycle in a downtrend is a movement started from Relative High going through consequent Relative Low and to consequent Relative High. The downtrend is considered broke when instead of installing a LH price goes to HH. In this case the movement from the most recent Low to a new Higher High will be the first major phase of a potential uptrend. As you see the last major phase of the downtrend is not followed by a corrective phase but is followed by the major phase on an uptrend. This means that the last downtrend cycle stays incomplete. That's why it is called half-cycle. ALL trends end in half-cycles.
expands in the major phases of a trend and contracts in corrective phases. If price installs a major phase but doesn't expand this indicates that we potentially have the last half-cycle of the trend. If expands in the major phase and then it expands even further during the corrective phase this indicates that this corrective phase will most likely turn into a major phase of an opposite trend.
The major phases of two adjucent cycles tend to show harmony both in amplitude and in time. , Pattern based on this phenomena. But corrective phases also tend to be equal in price and time. Reciprocal or Patterns exploit this phenomena. In the majority of cases major phases are steeper than corrective phases. This means that less bars required for a major phase to travel its amplitude than for a corrective phase to recover even the part of it.