Hello, Hans suggested a macro to draw the vectors . It works well but I find that in some situations, the arrow is too big. thank you, Fabrice
https://mailman.ntg.nl/pipermail/ntg-context/2016/085828.html \useMPlibrary[mat] \startMPextensions vardef math_stacker_arrow_shape = image ( drawarrow (OverlayWidth,OverlayOffset) -- (0,OverlayOffset) withcolor OverlayLineColor ; setbounds currentpicture to boundingbox currentpicture bottomenlarged (OverlayOffset/2) topenlarged (OverlayOffset/2) ; ) enddef ; vardef math_stacker_leftarrow_shape = math_stacker_arrow_shape enddef ; vardef math_stacker_rightarrow_shape = math_stacker_arrow_shape rotated 180 enddef ; \stopMPextensions \startuniqueMPgraphic{math:stacker:\number"2190} math_stacker_draw(math_stacker_leftarrow_shape) ; \stopuniqueMPgraphic \startuniqueMPgraphic{math:stacker:\number"2192} math_stacker_draw(math_stacker_rightarrow_shape) ; \stopuniqueMPgraphic % so far \setupmathstackers [both] % vfenced] [color=darkred, alternative=mp] \setupmathstackers [top] [color=darkred, alternative=mp] \setupmathstackers [bottom] [color=darkred, alternative=mp] \starttext $\overrightarrow {i}$ \stoptext
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