Began chapter 4, getting formula for general (possibly aperiodic) signal
x(t) = (1/2 \pi) \int X(jw) exp(jwt) dt   where X(jw) is the Fourier transform
X(jw) = \int x(t) exp(-jwt) dw. 
Computed several Fourier transforms.
Introduced sinc function, as Fourier transform of square pulse.
Noted the duality in computing Fourier/inverse Fourier transforms so that
the Fourier transform of a sinc function is a square pulse.
Obtained elementary properties (linearity, time-shift, conjugate) - their
effect on the Fourier transform.