Intersection of two sets of intervals

Hi,

Algorithm question: I have two sets of "intervals", where an interval is 
an ordered pair [a,b] of two numbers. Is there an efficient way in R to 
generate the intersection of two lists of same?

For concreteness: I'm representing a set of intervals with a data.frame:

 > list1 = as.data.frame(list(open=c(1,5), close=c(2,10)))
 > list1

  open close
1    1     2
2    5    10

 > list2 = as.data.frame(list(open=c(1.5,3), close=c(2.5,10)))
 > list2

  open close
1  1.5   2.5
2  3.0  10.0

How do I get the intersection which would be something like:
  open close
1  1.5   2.0
2  5.0  10.0

I wonder if there's some ready-built functionality that might help me 
out. I'm new to R and am still learning to vectorize my code and my 
thinking. Or maybe there's a package for interval arithmetic that I can 
just pull off the shelf.

Thanks,

-tom