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have to be more sketchy even than the preceding sections. We 
will concentrate on two aspects, namely the possibilities of 
decentralization of policy decisions and the question of the time 
order in which decisions must be made. Both depend on the 
mathematical structure of the model describing the relationships 
between the unknowns, that is, the policy parameters or instru- 
ment variables [6]. Decentralization, either with regard to 
sectors or with regard to regions, will be possible whenever a 
number of sectoral or regional parameters appear in a set of 
equations not containing parameters of other sectors and re- 
gions and sufficient in number to solve for the unknowns con- 
cerned. If it so happens that after a decision on some instru- 
ments further instruments occur in the same position, decisions 
on the latter must be taken after decisions on the former. Since 
the structure of the equations (or, if we like, the matrix of their 
coefficients) does not only depend on the relationships between 
the variables but also on the role given to some of them, it 
depends on the target and instrument variables, that is, on the 
type of policy, what possibilities for decentralization and what 
necessities as for time order there are. A simple example may 
illustrate our point. If targets are set for regional incomes — 
a case different from the ones so far discussed — the production 
volume of regional industries may be derived at once, provided 
we can assume a direct relation between regional income and 
production of regional industries. 
Among the most fascinating and pressing problems oi 
sectoral-cum-regional planning is the one whict forms of 
decentralization — whether sectoral or regional and what 
order of decisions is optimal [2]. Models of the class discussed 
in this paper mav teach us about these questions 
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Tinbergen - pag. 11