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Copulas, information, dependence and decoupling 199<br />

. . . , xn)−T(x1, . . . , xk−1, a, xk+1, . . . , xn), a < b. By integrability of the functions<br />

gi1,...,ic and condition A3 we obtain (I(·) denotes the indicator function)<br />

(8.3)<br />

δ 1 (a1,b1] δ2 (a2,b2] ···δn (an,bn] T(x1, . . . , xn)<br />

n�<br />

�<br />

= P(ai < ξi≤ bi) + E Un(ξi1, . . . , ξin)<br />

i=1<br />

n�<br />

�<br />

I(ai < ξi≤ bi) ≥ 0<br />

for all ai < bi, i = 1, . . . , n. 1 Right-continuity of T(x1, . . . , xn) and (8.1)–(8.3) imply<br />

that T(x1, . . . , xn) is a joint cdf of some r.v.’s X1, . . . , Xn with one-dimensional cdf’s<br />

Fk(xk), and the joint cdf T(x1, . . . , xn) satisfies (2.1).<br />

Let us now prove the sufficiency part. Consider the functions<br />

fi1,...,ic(xi1, . . . , xic) =<br />

c�<br />

s=2<br />

(−1) c−s<br />

�<br />

j1

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