diff --git a/debugging/lecture/debugging-chapter.pdf b/debugging/lecture/debugging-chapter.pdf
index d4df870..5faa385 100644
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diff --git a/pointprocesses/lecture/pointprocessscetchA.eps b/pointprocesses/lecture/pointprocessscetchA.eps
index 1dfe6f5..c1478a9 100644
--- a/pointprocesses/lecture/pointprocessscetchA.eps
+++ b/pointprocesses/lecture/pointprocessscetchA.eps
@@ -1,7 +1,7 @@
 %!PS-Adobe-2.0 EPSF-2.0
 %%Title: pointprocessscetchA.tex
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-%%CreationDate: Sat Nov 19 10:17:42 2016
+%%CreationDate: Tue Nov 14 09:22:04 2017
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@@ -430,10 +430,10 @@ SDict begin [
   /Title (pointprocessscetchA.tex)
   /Subject (gnuplot plot)
   /Creator (gnuplot 4.6 patchlevel 4)
-  /Author (jan)
+  /Author (benda)
 %  /Producer (gnuplot)
 %  /Keywords ()
-  /CreationDate (Sat Nov 19 10:17:42 2016)
+  /CreationDate (Tue Nov 14 09:22:04 2017)
   /DOCINFO pdfmark
 end
 } ifelse
diff --git a/pointprocesses/lecture/pointprocessscetchA.pdf b/pointprocesses/lecture/pointprocessscetchA.pdf
index b532798..2dcdf91 100644
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diff --git a/pointprocesses/lecture/pointprocessscetchB.eps b/pointprocesses/lecture/pointprocessscetchB.eps
index 1856ba8..f2ccaf3 100644
--- a/pointprocesses/lecture/pointprocessscetchB.eps
+++ b/pointprocesses/lecture/pointprocessscetchB.eps
@@ -1,7 +1,7 @@
 %!PS-Adobe-2.0 EPSF-2.0
 %%Title: pointprocessscetchB.tex
 %%Creator: gnuplot 4.6 patchlevel 4
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@@ -430,10 +430,10 @@ SDict begin [
   /Title (pointprocessscetchB.tex)
   /Subject (gnuplot plot)
   /Creator (gnuplot 4.6 patchlevel 4)
-  /Author (jan)
+  /Author (benda)
 %  /Producer (gnuplot)
 %  /Keywords ()
-  /CreationDate (Sat Nov 19 10:17:43 2016)
+  /CreationDate (Tue Nov 14 09:22:05 2017)
   /DOCINFO pdfmark
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diff --git a/pointprocesses/lecture/pointprocessscetchB.pdf b/pointprocesses/lecture/pointprocessscetchB.pdf
index 6e4e783..7fce211 100644
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diff --git a/spectral/lecture/spectral.tex b/spectral/lecture/spectral.tex
index 28d37d2..517e7aa 100644
--- a/spectral/lecture/spectral.tex
+++ b/spectral/lecture/spectral.tex
@@ -2,18 +2,35 @@
 
 This is a stub that should be filled :)
 
-\section{The Fourier space}
+% \section{The Fourier space}
 
 \section{The Fourier Transform}
+Complex numbers... magnitude and phase
 
 \subsection{Fast Fourier transform}
 
 \section{Power spectrum}
+\[ S_{x,x} = |X(f)|^2 \]
+
+Parceval theorem:
+\[ \int_{-\infty}^{+\infty} x(t)^2 dt = \int_{-\infty}^{+\infty} |X(f)|^2 df \]
+
+Autocorrelation:
+
+Wiener-Kinchin theorem:
+\[ {\cal F}\{Corr(x,x)\} = |X(f)|^2 \]
 
 \section{Spectrogram}
 
-\section{Transfer function}
+\section{Cross spectrum}
+\[ S_{x,y} = X(f)Y^*(f) \]
+is complex valued (magnitude and phase)!
 
-\section{Forward and reverse filter}
+Correlation theorem:
+\[ {\cal F}\{Corr(x,y)\} = X(f)Y^*(f) = S_{x,y} \]
+
+\section{Transfer function}
 
 \section{Coherence function}
+
+\subsection{Forward and reverse filter}