I don't know how to draw in Latex. Maybe someone has an idea how to make the diagram in the picture? Many thanks!
So here is my try:
\def\firstcircle{(0,0) circle (1.5cm)}
\def\secondcircle{(0:2cm) circle (1.5cm)}
\begin{tikzpicture}
\draw[filled] \firstcircle node {$n_{ij}$}
\secondcircle node {};
\node[anchor=south] at (current bounding box.north) {$t_i, t_j $};
\end{tikzpicture}
Do someone know how to write $t_i$ on the left side and $t_j$ on the right side?



tikzsolution. beside it exist solution with other packages, like pstrick etc. Your question is not very clear about this. Fortikzexiste exist good manual, where are also examples for Wenn diagrams. – Zarko Jul 18 '17 at 19:59