On 3/22/2021 9:40 AM, Petr Olsak wrote:

The \suppressmathparerror=1 should suppress \par errors in math mode. OK, this works:

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\suppressmathparerror=1 $$ a

b $$ \bye

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but the following example gives error: Display math should end with \Ustopdisplaymath

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\suppressmathparerror=1 $$ \halign{#\cr a\cr}

$$ \bye

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The LuaTeX manual does not exactly describes the behavior of this case. So, I don't know if this is feature or bug.

Note that the second example is primitive meaning of something like this:

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$$ \eqalignno{...}

$$

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If a user know that "empty lines are allowed in math mode" then he/she could leave empty line after \eqalignno too.

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