  By comparing 3 constituents of Orion A (gas, protostars, and
pre-main-sequence stars), both morhologically and kinematically, we derive the
following. The gas surface density near the integral-shaped filament (ISF) is
well represented by a power law, Sigma(b)=72 Msun/pc^2(b/pc)^{-5/8} for our
entire range, 0.05<b/pc<8.5, of distance from the filament ridge. Essentially
all protostars lie on the ISF or other filament ridges, while almost all
pre-main-sequence stars do not. Combined with the fact that protostars move <1
kms relative to the filaments while stars move several times faster, this
implies that protostellar accretion is terminated by a slingshot ejection from
the filaments. The ISF is the 3rd in a series of star bursts that are
progressively moving south, with separations of a few Myr in time and 3 pc in
space. This, combined with the filament's observed undulations (spatial and
velocity), suggests that repeated propagation of transverse waves thru the
filament is progressively digesting the material that formerly connected Orion
A and B into stars in discrete episodes. We construct an axially symmetric gas
density profile rho(r)=16 Msun/pc^3(r/pc)^{-13/8}. The model implies that the
observed magnetic fields are supercritical on scales of the observed
undulations, suggesting that the filament's transverse waves are magnetically
induced. Because the magnetic fields are subcritical on scales of the filament
on larger scales, the system as a whole is relatively stable and long lived.
Protostellar ejection occurs because the gas accelerates away from the
protostars, not the other way around. The model also implies that the ISF is
kinematically young, which is consistent with other lines of evidence. The
southern filament has a broken power law, which matches the ISF profile for
2.5<b/pc<8.5, but is shallower closer in. It is also kinematically older than
the ISF.
