\setupbackend[export=yes]

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    \startTEXpage
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            \reals {\mathbf R} \utfchar{"0211D} \utfchar{"1D411}
        \stopformula
        \setupmathematics[symbolset=blackboard-to-bold]
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            \reals {\mathbf R} \utfchar{"0211D} \utfchar{"1D411}
        \stopformula
    \stopTEXpage

\stoptext
