The smallest subdivision for which we have a formal macro
defined is a subsection.
Our choice has been to make subsections unnumbered and underlined.
When you type the command
subsection
{ subsec.heading }
you get the sort of heading which introduces this paragraph.
All of the control sequences,
chapter,
section and
subsection force the start of a new paragraph, so in principle
you do not have to skip lines as you type in text.
However, from the point of being able to proofread your
typed copy in order to make corrections, not skipping lines
can be a disaster.
The underlining of the text in the section macro is accomplished using
the control sequence
undertext { text }
This is a command worth knowing about, but in general using italics
is a better way to emphasize text.
This completes our discussion of the macros which handle the generation of titles for the major subdivisions of the usual paper.