ConTeXt: Math displays: eq. number and aligneq

[Tobias Burnus <burnus@gmx.de>]

Hi,

what's the best methode to typeset an equation number for a aligned
equation?

I found a \formulenummer (ConTeXt manual (Dutch), edition 960122, page
281), but this caused a lot of error messages with this few lines
(context-de, ConTeXt ver: 1999.2.1):

\platziereformel[-]
\startformel
\eqalignno{\overline P &= \frac{1}{T}\int\limits_0^T U_0I_0\cos^2\omega
t\,\dD t
         \qquad\hbox{mit $T=2\pi$}&\cr
 &=\frac{1}{2} U_0I_0.&{\formulenummer}\cr}
\stopformel

\bye
> ! Undefined control sequence.
> <argument> ...its _0^T U_0I_0\cos ^2\omega t\,\dD 
>                                                   t \qquad \hbox {mit $T=2\p...
> 
> \eqalignno ...\@lign ##$}\tabskip \z@skip \crcr #1
>                                                   \crcr }
> <argument> ...1}{2} U_0I_0.&{\formulenummer }\cr }
>                                                    
> \dodoplaatsformule ...lenummer }\dostartformula #4
>                                                   \dostopformula \else \doif...
> l.7 \stopformel

Tobias