First step is to draw the nodes and give them name. Lets start with the top node located at the origin and name it (top)
:
\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\node (top) at (0,0) {$\{x,y\}$};
\end{tikzpicture}
\end{document}
So now you have:
![enter image description here](https://i.stack.imgur.com/LB1Sn.png)
which is not too exciting.
Note: I included the full code here, but subsequent steps I show only the additions to the above to make it easier to follow.
Next, add the left and right nodes. These should be located relative to the (top)
node so that in case we decide to move the position of the top node, these two will move along with it:
\node [below left of=top] (left) {$x$};
\node [below right of=top] (right) {$y$};
So, now things a looking a bit more useful:
![enter image description here](https://i.stack.imgur.com/ZqHzh.png)
If these are not far enough apart, you could move them, again relatively, by using something like xshift=<length>
, or xshift=<length>
.
Next step is to draw the lines connecting these nodes via their node names (color used here to see the correspondence between the code and the output):
\draw [red, thick] (top) -- (left);
\draw [blue, thick] (top) -- (right);
to get:
![enter image description here](https://i.stack.imgur.com/cNC58.png)
If the lines are not long enough you can shorten then via a negative amount. For the top we use shorten <=-2pt
, and for the bottom shorten >=-2pt
to get:
![enter image description here](https://i.stack.imgur.com/3dG2R.png)
Using the to
syntax as opposed to the --
allows you to get fancier and control the angle at the out point via out=<angle>
, and the angle of the line coming in via in=<angle>
:
\draw [red, thick, shorten <=-2pt, shorten >=-2pt, out=-120, in=90] (top) to (left);
\draw [blue, thick, shorten <=-2pt, shorten >=-2pt, out=-60, in=90] (top) to (right);
which if it had been used below would have produced:
![enter image description here](https://i.stack.imgur.com/0bOlP.png)
As pointed out by Paul Gaborit, the out
and in
options are really only for the to
directive so some might prefer a syntax that more explicitly places those options for the to
as in:
\draw [red, thick, shorten <=-2pt, shorten >=-2pt] (top) to [out=-120, in=90] (left);
\draw [blue, thick, shorten <=-2pt, shorten >=-2pt] (top) to [out=-60, in=90] (right);
Best Answer
According to @barbarabeeton, here comes a possible PSTricks solution for the example you gave:
This gives the output: