diff --git a/20191128/gtk-4.c b/20191128/gtk-4.c
index 3e15b640a0f1503294f93bb69fa0b457d60288e4..132dbcb61fb979372da88225e8cb881d2b81a2d4 100644
--- a/20191128/gtk-4.c
+++ b/20191128/gtk-4.c
@@ -17,6 +17,7 @@ int main (int argc, char **argv)
   GtkWidget *drawing_area = gtk_drawing_area_new ();
   gtk_container_add (GTK_CONTAINER (vbox), drawing_area);
 
+  gtk_widget_show (drawing_area);
   gtk_widget_show (button);
   gtk_widget_show (vbox);
   gtk_widget_show (window);
diff --git a/20191128/gtk-5.c b/20191128/gtk-5.c
index 132dbcb61fb979372da88225e8cb881d2b81a2d4..c77feaac44766ae3e7b157d3a72e03f62c9c687b 100644
--- a/20191128/gtk-5.c
+++ b/20191128/gtk-5.c
@@ -16,6 +16,7 @@ int main (int argc, char **argv)
 
   GtkWidget *drawing_area = gtk_drawing_area_new ();
   gtk_container_add (GTK_CONTAINER (vbox), drawing_area);
+  gtk_widget_set_size_request (drawing_area, 100, 100);
 
   gtk_widget_show (drawing_area);
   gtk_widget_show (button);
diff --git a/20191128/higher-math-1.c b/20191128/higher-math-1.c
new file mode 100644
index 0000000000000000000000000000000000000000..62b6239b58c07468a8e675e3d6016ddbb0723d38
--- /dev/null
+++ b/20191128/higher-math-1.c
@@ -0,0 +1,9 @@
+#include <stdio.h>
+
+#define VIER 4
+
+int main (void)
+{
+  printf ("Drei mal vier = %d.\n", 3 * VIER);
+  return 0;
+}
diff --git a/20191128/higher-math-2.c b/20191128/higher-math-2.c
new file mode 100644
index 0000000000000000000000000000000000000000..e4c228d9793a09ce4884b8bbf284d371fa3bbffb
--- /dev/null
+++ b/20191128/higher-math-2.c
@@ -0,0 +1,9 @@
+#include <stdio.h>
+
+#define VIER vier
+
+int main (void)
+{
+  printf ("Drei mal vier = %d.\n", 3 * VIER);
+  return 0;
+}
diff --git a/20191128/higher-math-3.c b/20191128/higher-math-3.c
new file mode 100644
index 0000000000000000000000000000000000000000..11f51b66457848a3af2825e8bd5a5262671df2fc
--- /dev/null
+++ b/20191128/higher-math-3.c
@@ -0,0 +1,9 @@
+#include <stdio.h>
+
+#define VIER 4);
+
+int main (void)
+{
+  printf ("Drei mal vier = %d.\n", 3 * VIER
+  return 0;
+}
diff --git a/20191128/higher-math-4.c b/20191128/higher-math-4.c
new file mode 100644
index 0000000000000000000000000000000000000000..2be0072342a27850e35869964df2874b3908816f
--- /dev/null
+++ b/20191128/higher-math-4.c
@@ -0,0 +1,9 @@
+#include <stdio.h>
+
+#define VIER 4;
+
+int main (void)
+{
+  printf ("Drei mal vier = %d.\n", 3 * VIER);
+  return 0;
+}
diff --git a/20191128/higher-math-5.c b/20191128/higher-math-5.c
new file mode 100644
index 0000000000000000000000000000000000000000..ba0687bd87c9c5f5dd6354e311b4072ccb8c4fe6
--- /dev/null
+++ b/20191128/higher-math-5.c
@@ -0,0 +1,9 @@
+#include <stdio.h>
+
+#define VIER 2 + 2
+
+int main (void)
+{
+  printf ("Drei mal vier = %d.\n", 3 * VIER);
+  return 0;
+}
diff --git a/20191128/higher-math-6.c b/20191128/higher-math-6.c
new file mode 100644
index 0000000000000000000000000000000000000000..82fae73abc293a425a7295082f6effab1ebeed5d
--- /dev/null
+++ b/20191128/higher-math-6.c
@@ -0,0 +1,9 @@
+#include <stdio.h>
+
+#define VIER (2 + 2)
+
+int main (void)
+{
+  printf ("Drei mal vier = %d.\n", 3 * VIER);
+  return 0;
+}