breqn – Au­to­matic line break­ing of dis­played equa­tions

The pack­age pro­vides so­lu­tions to a num­ber of com­mon dif­fi­cul­ties in writ­ing dis­played equa­tions and get­ting high-qual­ity out­put. For ex­am­ple, it is a well-known in­con­ve­nience that if an equa­tion must be bro­ken into more than one line, ‘left...right’ con­structs can­not span lines. The breqn pack­age makes them work as one would ex­pect whether or not there is an in­ter­ven­ing line break.
The sin­gle most am­bi­tious goal of the breqn pack­age, how­ever, is to sup­port au­to­matic line­break­ing of dis­played equa­tions. Such line­break­ing can­not be done with­out sub­stan­tial changes un­der the hood in the way for­mu­lae are pro­cessed; the code must be watched care­fully, keep­ing an eye on pos­si­ble glitches.
The pack­age is (now) main­tained as part of the mh bun­dle of math­e­mat­i­cal type­set­ting sup­port pack­ages; the bun­dle also con­tains the flex­isym and math­style pack­ages, which are both des­ig­nated as sup­port for breqn.