  In the implosion conjecture, coronal loops contract as the result of magnetic
energy release in solar eruptions and flares. However, after almost two
decades, observations of this phenomenon are still rare, and most of previous
reports are plagued by projection effects so that loop contraction could be
either true implosion or just a change in loop inclination. In this paper, to
demonstrate the reality of loop contractions in the global coronal dynamics, we
present four events with the continuously contracting loops in an almost
edge-on geometry from the perspective of SDO/AIA, which are free from the
ambiguity caused by the projection effects, also supplemented by contemporary
observations from STEREO for examination. In the wider context of observations,
simulations and theories, we argue that the implosion conjecture is valid in
interpreting these events. Furthermore, distinct properties of the events allow
us to identify two physical categories of implosion. One type demonstrates a
rapid contraction at the beginning of the flare impulsive phase, as magnetic
free energy is removed rapidly by a filament eruption. The other type, which
has no visible eruption, shows a continuous loop shrinkage during the entire
flare impulsive phase which we suggest manifests the ongoing conversion of
magnetic free energy in a coronal volume. Corresponding scenarios are
described, which can provide reasonable explanations for the observations. We
also point out that implosions may be suppressed in cases when a
heavily-mass-loaded filament is involved, possibly serving as an alternative
account for their observational rarity.
