<s>
Retrenchment	B-Application
is	O
a	O
technique	O
associated	O
with	O
Formal	B-Architecture
Methods	I-Architecture
that	O
was	O
introduced	O
to	O
address	O
some	O
of	O
the	O
perceived	O
limitations	O
of	O
formal	O
,	O
model	O
based	O
refinement	O
,	O
for	O
situations	O
in	O
which	O
refinement	O
might	O
be	O
regarded	O
as	O
desirable	O
in	O
principle	O
,	O
but	O
turned	O
out	O
to	O
be	O
unusable	O
,	O
or	O
nearly	O
unusable	O
,	O
in	O
practice	O
.	O
</s>
