In a document, I use the subequations environment inside another subequations environment – to e.g. have equations numbered as (1a), (1b), (1ca), (1cb), (1d) etc. At an overall level, all the equations belong together, hence they all have number (1), and furthermore, at a nested level, the two (1c) equations belong together, hence (1ca) and (1cb). This all works fine, but the equations that then follow – which should be (2), (3) etc. – get different numbers. In the example below, the last equation outside all of the subequations should be number (2), but when I compile it it gets number (5).

I suppose there is some conflict causing the wrong numbering, but could anyone tell me how I obtain the correct numbering?

The code is as follows:

```
\documentclass[10pt,a4paper]{article}
\usepackage[latin1]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\begin{document}
\section{Section}
\begin{subequations}
These equations are numbered as subequations:
\begin{align}
F &= m a \\
p & = mv
\end{align}
These equations are also numbered as subequations, and they are numbered correctly:
% % %
\begin{subequations}
\begin{align}
F &= m a \\
p & = mv
\end{align}
\end{subequations}
\begin{subequations}
\begin{align}
F &= m a \\
p & = mv
\end{align}
\end{subequations}
\end{subequations}
But the next equation is then not numbered correctly; It should have number (2):
\begin{align}
F &= ma
\end{align}
\end{document}
```

## Best Answer

You should define a

`subsubequations`

environment: the problem is that at every`\begin{subequations}`

the "original" equation counter is stepped and its value is remembered to be restored at`\end{subequations}`

. Since in your document there are three`\begin{subequations}`

, the number of the next equation ends to be 5.