dot (graphviz): how to enforce position of nodes on x-axis?
I have a simple digraph that is supposed to represent a lattice - a graph where the nodes correspond to points in time and arcs represent words. Some 100 to 1000 nodes and about as many arcs.
Example structure:

For each node, I have an exact time stamp, so I would like to force dot to put the nodes on an exact position on the x-axis
Here is my toy example:
digraph {
  rankdir="LR";
  0 -> 1 [label="cat"]
  0 -> 2 [label="can"]
  1 -> 3 [label="is"]
  2 -> 3 [label="has"]
}

You can see it in an online dot editor here.
How can I define the position on the x-axis of nodes 1 and 2 (e.g. to make 2 appear further to the right than 1)?

Non trivial.  do you really want the X coordinate to be a function of the timestamp?  What about (long) pauses when nothing is happening?  This could make for a really wide graph.  Neato will let you specify X coordinate, but you need to specify Y also.
