E-field plots

Hello Steven et al,
I am trying to work through the defect1dsol.ctl example that is posted
on the nanophotonics course website in order to recreate the figure 4
that appears there and I am finding that I don't know how to get a
line plot of Ez from the h5 files.  I'm having trouble even getting
the condition satisfied that the frequency of one of the bands is
within the range of the minimum and maximum frequencies of the
structure without the defect.  Also, I'm not sure why the minimum and
maximum frequencies are defined by use of the following because I
don't know what car and cadr mean here (though I can see that this
gives the frequencies previously found for the two band case:
(define gap-min (car freqs))
(define gap-max (cadr freqs))

Any advice (hints as to where to look in the documentation?) would be
appreciated. Thanks.
Jim Andrews

-- 
James H. Andrews
Dept. of Physics & Astronomy
Youngstown State University