On Wednesday, August 5th, 2026 at 7:35 PM, Richard Kimberly Heck via lyx-users <[email protected]> wrote:
> There is > additional space above the displayed equation in the latter case. I take > it that this is in the inter-paragraph spacing. Please correct me if the > additional space is coming from somewhere else. But I get the same in > the latter case as if I'd written: > > test > > ~ > $$x=y$$ > You can trace what happens from the LuaTeX source (this is similar in other engines). When LuaTeX encounters a $ in vertical mode during the main control loop it runs run_new_graf(): https://gitlab.lisn.upsaclay.fr/texlive/luatex/-/blob/master/source/texk/web2c/luatexdir/tex/maincontrol.c#L860 which backs up one token, then runs new_graph(true): https://gitlab.lisn.upsaclay.fr/texlive/luatex/-/blob/master/source/texk/web2c/luatexdir/tex/maincontrol.c#L473 new_graph(true) create a new *indented* paragraph, and switch the mode to horizontal. https://gitlab.lisn.upsaclay.fr/texlive/luatex/-/blob/master/source/texk/web2c/luatexdir/tex/maincontrol.c#L1831 Since run_new_graf() backed up one token, back in the main control loop we encounter the same $ again but in horizontal mode: https://gitlab.lisn.upsaclay.fr/texlive/luatex/-/blob/master/source/texk/web2c/luatexdir/tex/maincontrol.c#L904 Now init_math() check the next token and if it is another math shift token we start a display equation: https://gitlab.lisn.upsaclay.fr/texlive/luatex/-/blob/master/source/texk/web2c/luatexdir/tex/texmath.c#L986 When LuaTeX start a display equation, it first checks the current paragraph. If it is empty (head==tail) it flushes it: https://gitlab.lisn.upsaclay.fr/texlive/luatex/-/blob/master/source/texk/web2c/luatexdir/tex/texmath.c#L1120 (LuateX specifically check more stuff here, such as local_par and direction nodes, these are LuaTeX specific). If it is not empty, It breaks it into lines and will add it to the vertical list eventually. Since you used $ in vertical mode, LuaTeX started an indented paragraph, i.e. a paragraph with a hbox node, so LuaTeX does not discard it, but it is visually empty and might seem like a vertical space. You can see the difference with \noindent $$x=y$$. In this case there is no indent box in the paragraph, so LuaTeX will discard it. Udi -- lyx-users mailing list [email protected] https://lists.lyx.org/mailman/listinfo/lyx-users
