A PhD thesis can often contain theorems, lemmas, definitions etc. The LaTeX kernel comes with the command:
which can be used to create an environment called <name> that has an optional argument. Each instance of the environment starts with <title> followed by the associated counter value. If <counter> is present, the new environment uses that counter instead of having a new counter defined for it. If <outer counter> is present, the environment counter is reset every time <outer counter> is incremented. The optional arguments are mutually exclusive.
In the example below, I've use
\newtheorem to define a new
environment called theorem, which has an associated
counter, also called theorem, that is dependant on the
The optional argument to the new environment can be used to add a caption. Modifying the above example (changes shown like this):
% later in the document:
This is an example of how to create a theorem-like environment.
This is another example of how to create a theorem-like environment.
Unfortunately there isn't a great deal of flexibility with the environment appearance. [Theorem bodies printed in a roman font]However there are various packages available that provide enhancements to this basic command, allowing you to adjust the appearance to suit your requirements. There seem to be two main contenders: amsthm and ntheorem. Both have advantages and disadvantages. For example, ntheorem is more flexible but amsthm is more robust. Therefore I'm going to describe both, and you will have to decide which one you prefer.
With both amsthm and ntheorem, you can still define new
theorem-like environments using
\newtheorem, but there is also
a starred version of that command, which can be used to define
unnumbered theorem-like environments.
Suppose I want to have an unnumbered remark environment, I can define the environment like this:
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