How do you skip subequation labels in LaTeX?

[ams2990]

I am trying to get subequations numbered nonsequentially. I have

\begin{subequations}
	\begin{equation}
		...
	\end{equation}
	\begin{equation}
		...
	\end{equation}
\end{subequations}

which gives me

(1a) ...
(1b) ...

Instead, I want (1c) instead of (1b). I have no clue whether this is trivial or requires me to use a different subequation method all together, I don't know. Any suggestions are acceptable, provided I am able to use it interchangeably with non-subequations, such as (1a),(1c),(2),(3),(4e),(4g),...

 

[cristo]

Why?

 

[Simon_Tyler]

It's not quite clear exactly what you want and why you want it - but you can probably do what you want by either making the occasional change to a counter or by defining a new environment and counter that counts the way you want.

To increment a counter, you use \addtocounter{\thecounter}{value}
To set a counter you use \setcounter{\thecounter}{value}

The counter for equations is \theequation and the counter for subequation is \thesubequation.

http://en.wikibooks.org/wiki/LaTeX/Advanced_Topics
http://texblog.wordpress.com/2007/07/25/counters-in-latex/