<s>
The	O
refinement	B-Application
calculus	I-Application
is	O
a	O
formalized	O
approach	O
to	O
stepwise	O
refinement	O
for	O
program	O
construction	O
.	O
</s>
<s>
In	O
the	O
latter	O
case	O
,	O
the	O
motivation	O
was	O
to	O
link	O
Abrial	O
's	O
specification	O
notation	O
Z	B-Language
,	O
via	O
a	O
rigorous	O
relation	O
of	O
behaviour-preserving	O
program	O
refinement	O
,	O
to	O
an	O
executable	O
programming	O
notation	O
based	O
on	O
Dijkstra	O
's	O
language	O
of	O
guarded	B-Application
commands	I-Application
.	O
</s>
