diff --git a/semester4/ps/ps-rb/main.pdf b/semester4/ps/ps-rb/main.pdf
index f3a4dfa..6d6939d 100644
Binary files a/semester4/ps/ps-rb/main.pdf and b/semester4/ps/ps-rb/main.pdf differ
diff --git a/semester4/ps/ps-rb/parts/00_prereq.tex b/semester4/ps/ps-rb/parts/00_prereq.tex
index 7821ad9..df30d9a 100644
--- a/semester4/ps/ps-rb/parts/00_prereq.tex
+++ b/semester4/ps/ps-rb/parts/00_prereq.tex
@@ -4,4 +4,9 @@
 $$
     s_n = a_1 \cdot \frac{1-q^n}{1-q} \qquad \underset{n\to\infty}{\lim} s_n = \frac{a_1}{1-q}
 $$
-\subtext{Wobei $a_i = a_1 \cdot q^{i-1}$}
\ No newline at end of file
+\subtext{Wobei $a_i = a_1 \cdot q^{i-1}$}
+
+\definition \textbf{Binomialkoeffizient}
+$$
+    \binom{n}{k} := \frac{n!}{k!\cdot(n-k)!}
+$$
\ No newline at end of file
diff --git a/semester4/ps/ps-rb/parts/04_joint-distributions.tex b/semester4/ps/ps-rb/parts/04_joint-distributions.tex
index 9d92f45..9ea0e5e 100644
--- a/semester4/ps/ps-rb/parts/04_joint-distributions.tex
+++ b/semester4/ps/ps-rb/parts/04_joint-distributions.tex
@@ -28,6 +28,18 @@ $$
 
 % good examples in script
 
+\theorem \textbf{Randverteilung}\\
+\smalltext{Die einzelnen Verteilungen $p_X$ lassen sich extrahieren:}\\
+\subtext{$\forall z \in W_i$:}
+$$
+ \P[X_i = z] = \underset{x_1,\ldots,x_{i-1},z,x_{i+1},\ldots,x_n}{\sum} p\Bigl( x_1,\ldots,x_{i-1},z,x_{i+1},\ldots,x_n \Bigr)
+$$
+\subtext{$X_1,\ldots,X_n$ diskret,$\quad$ gem. Vert. $p = \Bigl( p(x_1,\dots,x_n) \Bigr)_{x_1 \in W_1,\ldots,x_n \in W_n}$}
+
+{\footnotesize
+    \remark Nicht umgekehrt: Aus den Randverteilungen lässt sich nichts über die gem. Vert. schliessen.
+}
+
 \theorem \textbf{Erwartungswert}\\
 $$
     \E\Bigl[ \phi(X_1,\ldots,X_n) \Bigr] = \int_{-\infty}^\infty\cdots\int_{-\infty}^\infty\phi(x_1,\ldots,x_n)\cdot f(x_1\cdots x_n)\ dx_n\ldots dx_1