How can I write underscript within a line? When if I use double $$, then this is normal, $$H_1 = \bigcup_{\substack{j=1, \ j \neq 1}}^n ( H_1 \cap H_j )$$ But when I write it within a line , $H_1 = \bigcup_{\substack{j=1, \ j \neq 1}}^n ( H_1 \cap H_j )$ how strange, this is same mathjax code, wh...