[igraph] Shortest path between nodes i and j that must go through node k

[Margaux Le Cam]

Dear all,

I'm working on a colored graph with two types of labels, X and Y, where

X = { blue nodes } and Y = { red nodes }

I'm wondering if there is an algorithm which finds the shortest path between
the nodes i and j of X, which includes at least one node k of Y. More generally,
is it possible to find the shortest path between i and j, under the constraint that
this path goes through k ?

Thank you for any help

Margaux