148 
PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28 
where p is a constant that can be fixed arbitrarily in the interval 
(63) 
0<p<0,06 . 
The basic ID-system is a highly simplified demand-supply mo- 
del where instantaneous equilibrium is assumed, 
64) demand d, = supply s,=q, 
To bring out the characteristic differences as clearly as possible 
the primary forms of the models have heen constructed so as 
to differ only in one parameter, namely the coefficient of price p, 
in the demand relation. 
An ID- (or RFUE-) system. The primary form: 
d,=q = -3 p +U 
(6sa-b) | se t 11 
SMF ÉP-st Ou With E(g lp.) =~ 
> 
Diy 
The reduced form: 
(66a-b) 
pe —P Paty,» E@Ip_)y=-p pi; 
q:= = P_1 +97, »  E(glp_))= = Pr_1 
ind 
(67a-c) 
Ei 0120) = E(Uy Vg000) = E(u, V2) =0;  k=1, 2, .. 
The corresponding PFUE-system. The primary form: 
(68a-b) 
[7 —- 
i 
4 pet vy: with E(q;lh;)= - = 
Elglb,_1)= Zp 
£ 
2] Wold - pag. 34