A note on doubles of groups.

(With Nadia Benakli, Oliver T. Dasbach and Brian Mangum)

Abstract.

Recently, Rips produced an example of a double of two free groups which has unsolvable generalized word problem.
In this paper, we show that Rips's example fits into a large class of doubles of groups, each member of which contains (F_2 \times F_2)
and therefore has unsolvable generalized word problem and is incoherent.