How to create a chapter or part without starting a new page

In LaTeX, you can create a new chapter or part without starting a new page by \let\cleardoublepage\relax

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
\usepackage{xargs}  % add option arguments to \newcommand

% Create \chapter or \part without starting a new page.
\NewDocumentCommand{\unclear}{m}{
    \begingroup
        \let\cleardoublepage\relax
        #1
    \endgroup
}

% Create \mychapter without starting a new page.
%   - s: stared version, hide the heading number
%   - o: short ToC
%   - m: section text
%   - o: label
\NewDocumentCommand{\mychapter}{s o m o}{
    \begingroup
        \let\cleardoublepage\relax
        \IfBooleanTF{ #1 }{
            \chapter*{ #3 }
        }{
            \IfValueTF{ #2 }{
                \chapter[#2]{ #3 }
            }{
                \chapter{ #3 }
            }
        }

        \IfValueT{ #4 }{
            \label{ #4 }
        }
    \endgroup
}

Reference