r=1 lemma

LEMMA 2.4.5 Let .X; / be a log canonical pair, where X is a projective variety of dimension n. Let P i k ai Si be a decomposition. If KX and S1; S2; : : : ; Sk all generate the same ray of the cone of effective divisors and this ray is also spanned by an ample divisor, then $d=\sum a_i⩽n+1$.

(page) (Brown et al., 2018, p. 945)