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 x F_2 and therefore has unsolvable generalized word problem
and is incoherent.
Keywords:
doubles of groups, coherence, LERF, generalized word problem