Systeme is so far the niftiest package for systems of equation as the syntax can be very short. BUT it's horribly restrictive: Just switching the unknowns to, say, I_1, I_2 and I_3 to print a electric circuit problem is tedious (haven't succeeded yet), and it doesn't allow repetitions of same unknowns. I have to, for example, type an equation A+A=2, but this seems to be forbidden as systeme demands the general matrix form.

The whole topic of typing systems of equations is a central one in mathematical typesetting, so I'm amazed I haven't seen a proper all-around solution yet. Cases environment won't do as that's not what it's for, align environment is missing the big brace and adding need extra packages which at least for me lead to contradicting packages.

Is there a new, "better" systeme available? Or do I just have to wait for LaTeX3 to solve this problem natively?

Something as simple as

\documentclass[a4paper]{article}
\usepackage{systeme}
\begin{document}
\systeme[AB][;]{A+A=2;A+B=3}
\end{document}


should be manageable easily, surely.

• If you are so sure it is so easy, you should solve the problem and publish your solution on CTAN. And I don't know what you would count as L3 solving it natively, but you can use the L3 stuff in L2 already, so you don't have to wait. – cfr Dec 28 '16 at 4:14

Yes, it would be great to walk into the store and pick what you want, for the price that you want; the best of both worlds...

...until then, the only thing you're forfeiting by sticking to systeme is ease of input, but you're giving up the flexibility that you want. empheq provides this flexibility with the addition of some keystrokes: \documentclass{article}

\usepackage{systeme,empheq}

\begin{document}

$\systeme[AB][;]{A=2;A+B=3}$

\begin{empheq}[left=\empheqlbrace]{align*}
\strut A + A &= 2 \\
\strut A + B &= 3
\end{empheq}

\end{document}

• I don't quite follow the second paragraph. Are you saying that systeme has the con of easy input and the con of inflexibility (so the first is not the only downside)? Or is easy input a pro and inflexibility a con, which empheq reverses? – cfr Dec 28 '16 at 21:18
• @cfr: systeme provides easy input (a pro) but at the (current) loss of flexibility (a con). – Werner Dec 29 '16 at 1:00
• So you should say something like ...until then, the only thing you're gaining by sticking to systeme is ease of input, but you're giving up the flexibility that you want. Or ...until then, the only thing you're forfeiting by giving up systeme is ease of input, but you're then able to have the flexibility that you want. – cfr Dec 29 '16 at 1:40

You can have a look at autoaligne, by the same author as systeme.

\documentclass[a4paper]{article}
\usepackage{autoaligne}
\begin{document}
\left\{\autoaligne{A+A=2\\A+B=3\\A++C=9}\right.
\end{document} 