[igraph] enumerating triads of certain type?

[baidao]

Hi,

I am new to igraph. I searched the mailing list archive but did not
get an answer, so I'd propose it here.

By using triad.census() I could get the numbers of 16  triads types.
But how to enumerate all triads of a certain type? e.g., I want igraph
to list all the vertexes of the triad type 'A->B->C'.

Best,

baidao