[igraph] how do I get 'from' and 'to' of an edge?

[Sam Steingold]

I have a graph in R:
Vertices: 2 
Edges: 2 
Directed: TRUE 
Edges:
                                            
[0] '4f33629f41393d3d' -> '4f54f25aaf86e815'
[1] '4f33629f41393d3d' -> '4f33629f41393d3d'

How do I get the _set_ of sources (and destinations) of all edges?
I can get all edges as E(g), and individual edges as E(g)[0..1], but how
do I get the source and destination (from & to) of an edge?
"Vertex and edge sequences and iterators" doc mentions 'from' and 'to'
"special functions", but I cannot figure out how to use them.

Thanks!

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Sam Steingold (http://sds.podval.org/) on Ubuntu 11.10 (oneiric) X 11.0.11004000
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