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-rw-r--r--system/doc/efficiency_guide/commoncaveats.xml48
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diff --git a/system/doc/efficiency_guide/commoncaveats.xml b/system/doc/efficiency_guide/commoncaveats.xml
index c1d71e745a..854dd54660 100644
--- a/system/doc/efficiency_guide/commoncaveats.xml
+++ b/system/doc/efficiency_guide/commoncaveats.xml
@@ -169,53 +169,5 @@ multiple_setelement(T0) ->
{Bin1,Bin2} = split_binary(Bin, Num)</code>
</section>
- <section>
- <title>Operator "--"</title>
- <p>The "<c>--</c>" operator has a complexity
- proportional to the product of the length of its operands.
- This means that the operator is very slow if both of its operands
- are long lists:</p>
-
- <p><em>DO NOT</em></p>
- <code type="none"><![CDATA[
- HugeList1 -- HugeList2]]></code>
-
- <p>Instead use the <seealso marker="stdlib:ordsets">ordsets</seealso>
- module in STDLIB:</p>
-
- <p><em>DO</em></p>
- <code type="none">
- HugeSet1 = ordsets:from_list(HugeList1),
- HugeSet2 = ordsets:from_list(HugeList2),
- ordsets:subtract(HugeSet1, HugeSet2)</code>
-
- <p>Obviously, that code does not work if the original order
- of the list is important. If the order of the list must be
- preserved, do as follows:</p>
-
- <p><em>DO</em></p>
- <code type="none"><![CDATA[
- Set = gb_sets:from_list(HugeList2),
- [E || E <- HugeList1, not gb_sets:is_element(E, Set)]]]></code>
-
- <note><p>This code behaves differently from "<c>--</c>"
- if the lists contain duplicate elements (one occurrence
- of an element in HugeList2 removes <em>all</em>
- occurrences in HugeList1.)</p>
- <p>Also, this code compares lists elements using the
- "<c>==</c>" operator, while "<c>--</c>" uses the "<c>=:=</c>" operator.
- If that difference is important, <c>sets</c> can be used instead of
- <c>gb_sets</c>, but <c>sets:from_list/1</c> is much
- slower than <c>gb_sets:from_list/1</c> for long lists.</p></note>
-
- <p>Using the "<c>--</c>" operator to delete an element
- from a list is not a performance problem:</p>
-
- <p><em>OK</em></p>
- <code type="none">
- HugeList1 -- [Element]</code>
-
- </section>
-
</chapter>