ABSTRACT
Theorem 1 . Let T be a summant on a figure K such that JK |T| = 0. Then JK \fT \ = 0 for every function f on K .
P roof. Apply Theorem 1 (§1.7) with νσ = |/ |, υ, = 1 for i = 1 , 2,· · · , and 5 = |T| to get JK \fT \ = Σ Ζ ι Ι κ \ Τ \ = 0 according to (7)(§1.7). □
Recall that a function on a set K is the indicator 1 E of a subset E of K if l E{t) = 1 for t in E , 0 for t in K — E.
