sed '/@inlineifset/,/^ *$/!d;
  s/@inlineifset{mrg, @btpar{@//' $flnm >> $ofln

@section Correlations between
seismograms,,,,}}

@inlineifset{mrg, @ptpar{Most common use of ambient noise is subsurface
tomography [extract traveltimes of Rayleigh Wavetrains].,,,,}}

@inlineifset{mrg, @ctpar{(1) cross correlation of waveforms;, (2)
computation of group and phase velocities at different wave frequencies
(periods),,,}}

@inlineifset{mrg, @ptpar{?,,,,}}

@section Correlations between seismograms

@inlineifset{mrg, @ptpar{Most common use of ambient noise is subsurface
tomography [extract traveltimes of Rayleigh Wavetrains].,,,,}}

@inlineifset{mrg, @ctpar{(1) cross correlation of waveforms;, (2)
computation of group and phase velocities at different wave frequencies
(periods),,,}}

@inlineifset{mrg, @ptpar{?,,,,}}

cat file

@inlineifset{mrg, @btpar{@@section Correlations between
Seismograms,,,,}}

@inlineifset{mrg, @ptpar{Most common use of ambient noise is subsurface
tomography [extract traveltimes of Rayleigh Wavetrains].,,,,}}

@inlineifset{mrg, @ctpar{(1) cross correlation of waveforms;, (2)
computation of group and phase velocities at different wave frequencies
(periods),,,}}

The most common approach in the ambient noise technique is to extract
the traveltimes of background Rayleigh Wavetrains using the cross
correlation of waveforms, followed by the computation of group and phase
velocities at different wave frequencies (periods)
@ref{bibl--Ermert--et--Villasenor--et--Fichtner--2016,, Ermert@comma{}
Villase@~nor & Fichtner (2016)}.  The geophysical basis is that when
diffuse wavefields are produced by diffuse sources or by multiple
scatterers, although the station instruments detect random signals, when
the same seismic wavetrain passes through two distinct stations, the
recorded seismograms are weakly correlated.  This emerged from one of
the most well known conjectures in seismology @minus @ @dfn{The
Claerbout Cross Correlation Conjecture}.  It was first stated by
American Geophysicist Jon F.@: Claerbout in 1968, after showing that the
reflectivity response of a one dimensional (1D) layered structure from a
surface source and a surface receiver is one side of the autocorrelation
of the seismogram recorded at the same surface receiver but transmitted
from a source at depth.

@inlineifset{mrg, @ptpar{?,,,,}}

It was specialist discipline of @dfn{Helioseismology}, developed in
recent decades that validated the long standing geophysical cross
correlation approach that generalised Claerbout's Conjecture to Three
Dimensions (3-D).  Essentially, helioseismology studies the surface
oscillations of the sun in a timescale of minutes and hours as seen from
solar spectra (spectral lines).  The fundamental physics for working
with the surface undulations of the sun focuses on the simulation
(modelling) of acoustic wave propagation stochastically excited and
damped by the convection of solar plasma (e.g., using P-Modes).