You obviously didn't read my first mailing correctly and copied an incomplete version of my MWE. The definitions of \Up and \Dn are right there before \starttext.  Whether the mathmatrix is empty of not does not make a difference.  For the sake of completeness I present you a different MWE below which incorporates your requested changes.  Fails with 2017.09.07 23:44 (It worked before, so your version 2017.09.05 15:10 seems to be unaffected). --- \starttext \startformula   \startmathalignment     \NC \psi_{+,\mathord\Uparrow} ...     \startmathmatrix       \NC 0 \NC 1 \NR       \NC 1 \NC 0 \NR     \stopmathmatrix     \NR     \NC \psi_{+,\mathord\Downarrow} ...     \NR   \stopmathalignment \stopformula \stoptext On Fri, 2017-09-08 at 11:24 +0200, Otared Kavian wrote:

Hi Henri,

I think your code has a problem: the first one is that the definition of \Up and \Down is not understood when I compile your example, and then you introduce an empty mathmatrix which creates a difficulty too. Once I remove the definitions of \Up and \Dn  the code is typeset (ConTeXt  ver: 2017.09.05 15:10 MKIV beta). Can you please give a more detailed example where you see the problem?

Best regards: OK

...

On 8 Sep 2017, at 06:51, Henri wrote:

\define\Up{\mathord\Uparrow} \define\Dn{\mathord\Downarrow}

\starttext

\placeformula \startformula   \startmathalignment     \NC \psi_{+,\Up} ...     \startmathmatrix     \stopmathmatrix     \NR     \NC \psi_{+,\Dn} ...     \NR   \stopmathalignment \stopformula

\stoptext

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