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There really is no convention for indicating the end of things in text. You are asking for a way to move up the hierarchy of the document without a title to indicate the change. There really isn't ...
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#4: Attribution notice removed
Source: https://writers.stackexchange.com/a/23566 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#3: Attribution notice added
Source: https://writers.stackexchange.com/a/23566 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
There really is no convention for indicating the end of things in text. You are asking for a way to move up the hierarchy of the document without a title to indicate the change. There really isn't a reliable way to indicate that to a reader. Titles indicate the beginning of things not the end of things. What there is a convention for is creating a subjection that is a summation of the entire chapter. The name of that subsection is generally "Conclusion". A concluding section is not really returning to the main level. The reader is too far removed from what they read in the main level for it simply to resume. Rather, the concluding section is a subsection that reviews the subject matter of the whole chapter. This is not a perfectly symmetrical or hierarchical design, but then text is not really hierarchical at all. It really is linear. The reader cannot receive it in any form other than linear, and in many texts, headings do not occur in a strict order of hierarchy. Rather, the act more like road signs: a large sign to announce you are entering a large town; a small sign to indicate you are entering a village. So don't think of a text as a hierarchy, but as a sequence with sign posts which may or may not follow a hierarchical sequence. Your concluding section, which summarizes the argument of the whole chapter, deserves a heading that announces it as such.