having $$1+2=3\eqno(1)$$ $$1+2=3\eqno(1)$$ $$1+2=3\eqno(1)$$ $$1+2=3\eqno(1)$$ $$1+2=3\eqno(1)$$ $$1+2=3\eqno(1)$$ $$1+2=3\eqno(1)$$ $$1+2=3\eqno(1)$$ $$1+2=3\eqno(1)$$ \end as the example document and running pdftex and luatex on it, it makes clear that with space between equations is too much when compiled with luatex. both PDFTeX and LuaTeX outputs are attached. -- Vafa