Arithmetic of Fuzzy Sets
Andrzej Piegat · Studies in fuzziness and soft computing · 2001
Fuzzy numbers may be applied, for example, in the modeling of a system of a known input/output mapping given in terms of a conventional mathematical model y = f (X), where the input signals cannot be measured precisely but only approximately, e.g.: $$\begin{array}{*{20}{c}} {{x_1} = approx.9,}\\ {{x_1} = approx.10,}\\ {y = {x_1} + {x_2}.} \end{array}$$ .