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Math and science::Analysis::Tao::09. Continuous functions on R

Arithmetic operations on functions

Given two functions \( f : X \to \mathbb{R} \) and [...], we can define their:

sum, \( f + g : X \to \mathbb{R} \)
\( (f + g)(x) := f(x) + g(x) \)
difference, \( f - g : X \to \mathbb{R} \)
\( (f - g)(x) := f(x) - g(x) \)
maximum, \( \max(f, g) : X \to \mathbb{R} \)
\( \max(f, g)(x) := \max(f(x), g(x)) \)
minimum, \( \min(f, g) : X \to \mathbb{R} \)
\( \min(f, g)(x) := \min(f(x), g(x)) \)
product, \( fg : X \to \mathbb{R} \) (or \( f \cdot g \) )
\( (fg)(x) := f(x)g(x) \)
quotient, assuming \( g(x) \ne 0 \text{ for all } x \in X\), \( f/g : X \to \mathbb{R} \)
\( (f/g)(x) := f(x)/g(x) \)
constant multiple, \( cf : X \to \mathbb{R} \)
\( (cf)(x) := cf(x) \)