subeqn – Pack­age for sube­qua­tion num­ber­ing

Some­times it is nec­es­sary to be able to re­fer to subex­pres­sions of an equa­tion. In or­der to do that these subex­pres­sions should be num­bered. In stan­dard LaTeX there is no pro­vi­sion for this. To solve this prob­lem Stephen Gildea once wrote subeqn.sty for LaTeX 2.09; Don­ald Arse­nau rewrote the macros and Jo­hannes Braams made them avail­able for LaTeX2ε.
Note that this pack­age is not com­pat­i­ble with the pack­age sube­q­nar­ray (writ­ten by Jo­hannes Braams), but it can be used to­gether with the LaTeX class op­tions leqno and fleqn.