What is equivalent of latex math aligned in ConTeXt?

[Xan <dxpublica@telefonica.net>]

Hi,

I read the document "Using \startalign and friends" of Aditya (that it's 
good) and I can't find anything under ams aligned. Is this an equivalent 
in ConText?

For example, what is the equivalent of:

\begin{equation*}
\left.\begin{aligned}
 & 2^2 | n_0\\
 & 4^2 | n_0 + 2 \Rightarrow (2^2)^2 | n_0 +2 \Rightarrow 2^2 | n_0 +2 
\text{ ya que } 2^2 | (2^2)^2
\end{aligned}\right\} \Rightarrow 2^2 | (n_0 + 2 - n_0) \Rightarrow 2^2 | 2
\end{equation*}

in ConTeXt?

I tried something like:

\startformula
\startmathalignment
 \NC \startaligned
\NC \lambda_{0, \lvert k - s \rvert} (n) \NC < f(n) \NR
\NC \text{ per a $n$ suficientment gran } \NC \NR
\stopaligned \NC  \iff
\startaligned
\NC \lambda_{s, k} (n) \NC < f(n) \NR
\NC \text{ per a $n$ suficientment gran } \NC \NR
\stopaligned \NR[+]
 \NC \lambda_{s, k} (n) < f(n) \text{ per a $n$ suficientment gran } \NC 
\iff  \lambda_{0, \lvert k - s \rvert} (n) < f(n) + C \text{ per a $n$ 
suficientment gran }  \NR[+]
\stopmathalignment
\stopformula

but " Undefined control sequence" appears to me.

Thanks a lot,
Xan.

PS: Please CCme
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