Splitting the input

Divide and conquer—this could be our motto now. We will figure out how to break down a document into several sub-documents. Thus, while we are writing, we will be able to manage a huge project consisting of many chapters in separate files.

Firstly, we will separate settings and body text by swapping out the preamble. Secondly, we will write chapters in separate files and include them afterward.

We will begin to write a detailed document regarding equations and equation systems. The result should be in the style of a thesis or a book. We can use the last example of Chapter 9, Writing Math Formulas, where we dealt with theorems concerning equations.

We will create several files, step by step:

1. Create a new document. Inside this, load all the packages and specify the options, like we did in our preambles in the previous chapters. Use all the beneficial packages that we have already learned about:

   \usepackage[english]{babel} 
   \usepackage[T1]{fontenc...