diff --git a/20191212/Makefile-0 b/20191212/Makefile-0
new file mode 100644
index 0000000000000000000000000000000000000000..cc29dc9f8d2298b455e310e1a713fb4f704e0716
--- /dev/null
+++ b/20191212/Makefile-0
@@ -0,0 +1,8 @@
+hello-6: hello-6.o pruzzel.o
+	gcc hello-6.o pruzzel.o -o hello-6
+
+hello-6.o: hello-6.c
+	gcc -Wall -O hello-6.c -c
+
+pruzzel.o: pruzzel.c
+	gcc -Wall -O pruzzel.c -c
diff --git a/20191212/Makefile-1 b/20191212/Makefile-1
new file mode 100644
index 0000000000000000000000000000000000000000..78042b9f4f3c63a0ef2c70bbc2844f046c577ee8
--- /dev/null
+++ b/20191212/Makefile-1
@@ -0,0 +1,8 @@
+hello-6: hello-6.o pruzzel.o
+	gcc hello-6.o pruzzel.o -o hello-6
+
+hello-6.o: hello-6.c pruzzel.h
+	gcc -Wall -O hello-6.c -c
+
+pruzzel.o: pruzzel.c pruzzel.h
+	gcc -Wall -O pruzzel.c -c
diff --git a/20191212/Makefile-2 b/20191212/Makefile-2
new file mode 100644
index 0000000000000000000000000000000000000000..9c5c4bc67471500842f3d1ee985ced87265ab592
--- /dev/null
+++ b/20191212/Makefile-2
@@ -0,0 +1,13 @@
+TARGET = hello-6
+OBJECTS = hello-6.o pruzzel.o
+HEADERS = pruzzel.h
+CFLAGS = -Wall -O
+
+$(TARGET): $(OBJECTS)
+	gcc $(OBJECTS) -o $(TARGET)
+
+%.o: %.c $(HEADERS)
+	gcc $(CFLAGS) $< -c
+
+clean:
+	rm -f $(OBJECTS) $(TARGET)
diff --git a/20191212/blink-3.c b/20191212/blink-3.c
new file mode 100644
index 0000000000000000000000000000000000000000..5268e7977f0f2a99b2005a81a2fa7560dfea481f
--- /dev/null
+++ b/20191212/blink-3.c
@@ -0,0 +1,17 @@
+#include <avr/io.h>
+
+#define F_CPU 16000000
+#include <util/delay.h>
+
+int main (void)
+{
+  DDRD = 0x01;
+  PORTD = 0x01;
+  while (1)
+    {
+      while ((PIND & 0x02) == 0)
+        ; /* just wait */
+      PORTD ^= 0x01;
+    }
+  return 0;
+}
diff --git a/20191212/hello-6.c b/20191212/hello-6.c
new file mode 100644
index 0000000000000000000000000000000000000000..c160a51f7a3c73664fdc20dd3a21429a77142644
--- /dev/null
+++ b/20191212/hello-6.c
@@ -0,0 +1,7 @@
+#include "pruzzel.h"
+
+int main (void)
+{
+  pruzzel ("Hello, world!\n");
+  return 0;
+}
diff --git a/20191212/hp-20191212.pdf b/20191212/hp-20191212.pdf
index 4d32b5eeef4a26ea6addd0af097bd075b7c0672c..fb871bfd2d50562bc0429b3c25e19c07eaf1e75f 100644
Binary files a/20191212/hp-20191212.pdf and b/20191212/hp-20191212.pdf differ
diff --git a/20191212/hp-20191212.tex b/20191212/hp-20191212.tex
index b1c85d58d59da9cbb52ef05266943b55716687d6..a44fb1c291aa53c0dec848b17f53ee903a2a4b2c 100644
--- a/20191212/hp-20191212.tex
+++ b/20191212/hp-20191212.tex
@@ -524,6 +524,8 @@
 
 \end{frame}
 
+\iffalse
+
 \subsection{Binärdarstellung negativer Zahlen}
 
 \begin{frame}[fragile]
@@ -709,4 +711,6 @@
 
 \end{frame}
 
+\fi
+
 \end{document}
diff --git a/20191212/make-1.txt b/20191212/make-1.txt
new file mode 100644
index 0000000000000000000000000000000000000000..a60f52923804359e83ecd9bd38f33d16f73b3830
--- /dev/null
+++ b/20191212/make-1.txt
@@ -0,0 +1,33 @@
+cassini/home/peter/bo/2019ws/hp/20191212> cat Makefile
+hello-6: hello-6.o pruzzel.o
+        gcc hello-6.o pruzzel.o -o hello-6
+
+hello-6.o: hello-6.c
+        gcc -Wall -O hello-6.c -c
+
+pruzzel.o: pruzzel.c
+        gcc -Wall -O pruzzel.c -c
+cassini/home/peter/bo/2019ws/hp/20191212> make
+make: „hello-6“ ist bereits aktuell.
+cassini/home/peter/bo/2019ws/hp/20191212> rm hello-6
+cassini/home/peter/bo/2019ws/hp/20191212> make
+gcc hello-6.o pruzzel.o -o hello-6
+cassini/home/peter/bo/2019ws/hp/20191212> rm hello-6 *.o
+cassini/home/peter/bo/2019ws/hp/20191212> make
+gcc -Wall -O hello-6.c -c
+gcc -Wall -O pruzzel.c -c
+gcc hello-6.o pruzzel.o -o hello-6
+cassini/home/peter/bo/2019ws/hp/20191212> ./hello-6
+Hello, world!
+cassini/home/peter/bo/2019ws/hp/20191212> ls -l pruzzel.c
+-rw-r--r-- 1 peter peter 89 Nov 21 17:08 pruzzel.c
+cassini/home/peter/bo/2019ws/hp/20191212> touch pruzzel.c
+cassini/home/peter/bo/2019ws/hp/20191212> ls -l pruzzel.c
+-rw-r--r-- 1 peter peter 89 Dez 12 16:26 pruzzel.c
+cassini/home/peter/bo/2019ws/hp/20191212> make
+gcc -Wall -O pruzzel.c -c
+gcc hello-6.o pruzzel.o -o hello-6
+cassini/home/peter/bo/2019ws/hp/20191212> mv -i Makefile Makefile-1
+cassini/home/peter/bo/2019ws/hp/20191212> make -f Makefile-1
+make: „hello-6“ ist bereits aktuell.
+cassini/home/peter/bo/2019ws/hp/20191212>
diff --git a/20191212/pruzzel.c b/20191212/pruzzel.c
new file mode 100644
index 0000000000000000000000000000000000000000..a03f3ffc532054611cad3d9e137ccd973c874399
--- /dev/null
+++ b/20191212/pruzzel.c
@@ -0,0 +1,7 @@
+#include <stdio.h>
+
+int pruzzel (const char *bla)
+{
+  printf ("%s", bla);
+  return 42;
+}
diff --git a/20191212/pruzzel.h b/20191212/pruzzel.h
new file mode 100644
index 0000000000000000000000000000000000000000..5b56ad93ce5dfca18c86f429c2b7d34a3cf01f6c
--- /dev/null
+++ b/20191212/pruzzel.h
@@ -0,0 +1 @@
+extern int pruzzel (const char *bla);
diff --git a/hp-slides-2019ws.pdf b/hp-slides-2019ws.pdf
index b77c320868c3c86b2f19a89b61c8fcd0b0570a54..43b76c37b03ad405f04243ed2fac44a0852a9fc9 100644
Binary files a/hp-slides-2019ws.pdf and b/hp-slides-2019ws.pdf differ