overlap different line in a xyplot (lattice)

Peter Ehlers <ehlers <at> ucalgary.ca> writes:

On 2010-12-10 07:04, Francesco Nutini wrote:

dear [R] users,
is there a way to plot different data (but with the same x-variables) 

in the same xyplot window?

There are already a similar question, but the answer is 

not enought explanatory...

Something like this?

[snip]


 Also possibly the layer() command in the latticeExtra package.

  If there is an answer that doesn't make sense to you it might
be most efficient to post an edited version of that question/answer,
attempting to clarify which parts of the answer you do and don't
understand ...

  A reproducible example would be nice too.

  Ben Bolker