<p>On page 543 of the textbook <em>Further Mathematics for Economic Analysis</em> (second edition), the definition of (direct) image is the following:</p>
<p>Let <span class="math-container">$f: A \rightarrow B$</span> be a function. The (direct) image under <span class="math-container">$f$</span> of a subset <span class="math-container">$S$</span> of <span class="math-container">$A$</span> is the set</p>
<p><span class="math-container">$f(S) = \{y \in B: y = f(x) \space \text{for some} \space x \in A\}$</span></p>
<p>I feel like we should say &quot;for some <span class="math-container">$x \in S \subseteq A$</span>&quot; instead. So I am just wondering if it is a typo?</p>

CC BY-SA 4.0
2024-06-26T03:55:42.473Z
I think you are right, it seems like a typo.
teddi
CC BY-SA 4.0
2024-06-26T12:58:48.947Z
Definitely a typo.
VARulle
<mathematical-economics><definition>
Is this a typo in Sydsaeter's book of image definition?
Shujun Tan
# Is this a typo in Sydsaeter's book of image definition?

(Asked by: username_0 on 2024-06-25)

On page 543 of the textbook *Further Mathematics for Economic Analysis* (second edition), the definition of (direct) image is the following:

Let $f: A \rightarrow B$ be a function. The (direct) image under $f$ of a subset $S$ of $A$ is the set

$f(S) = \{y \in B: y = f(x) \space \text{for some} \space x \in A\}$

I feel like we should say "for some $x \in S \subseteq A$" instead. So I am just wondering if it is a typo?

**Tags:** mathematical-economics, definition
> **Comments:**
> **username_1**: I think you are right, it seems like a typo.  
> **username_2**: Definitely a typo.  

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## 0 answers

