A simple alternative to tikz is the usage of \framed.

\define[1]\oldfact
  {\inmframed[frame=off,strut=no,leftframe=on,bottomframe=on]{#1}}

\starttext

\m{\oldfact{n}}

\stoptext

Wolfgang

Thanks a lot. It should work nicely.

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Respect,

Shiv Shankar Dayal