:: deftheorem defines f-convex FUZNUM_1:def 5 :
for F being FuzzySet of REAL holds
( F is f-convex iff for x1, x2, l being Real st 0 <= l & l <= 1 holds
F . ((l * x1) + ((1 - l) * x2)) >= min ((F . x1),(F . x2)) );