The real question is why do you get an index without two columns.

\starttext

\dorecurse{26}{\convertnumber{a}{#1}\expanded{\index{\convertnumber{a}{#1}}}}

\placeregister[index]%[n=3]

\stoptext



Hans van der Meer schrieb am 26.08.18 um 17:37:
> How do I produce an index with more than one column?
>
> This produces one column only:
> \startchapter[title=\mytitle{Register}]
> \startcolumns[n=2]
> \placeregister[index]
> \stopcolumns
>
> Nor did \placeregister[index][n=2] or \placeindex[n=2], with or 
> without the columns envirenment, produce the result wanted.
> The \startsimplecolumns[n=2] environment did produce two columns, but 
> then played havoc with the textheight.
>
> dr. Hans van der Meer
>
>
>
>
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