Rules / Build

Double subscript — Double subscript or superscript

A symbol has two subscripts (or superscripts), such as w_i_j.

Fix

Group them in braces: w_{ij}.

Example

Reproduced on TeX Live 2026 by CI · pdflatex · corpus/double-subscript

Two subscripts on one symbol

Fails: main.tex
\documentclass{article}
\begin{document}
The weight $w_i_j$ connects neuron $i$ to neuron $j$.
\end{document}
Fixed
\documentclass{article}
\begin{document}
The weight $w_{ij}$ connects neuron $i$ to neuron $j$.
\end{document}
What TeX prints in main.log
! Double subscript.
l.3 The weight $w_i_
                    j$ connects neuron $i$ to neuron $j$.
I treat `x_1_2' essentially like `x_1{}_2'.