TeX Quellcode:

\begin{array}{crcrcrcrcl} \text{I} & 4a &+& 2b &+& 1 &=& 1 &\vert& -1 \cr \text{II} & a &+& b &+& 1 &=& 2 &\vert& -1 \cr \cr \text{I} & 4a &+& 2b & & &=& 0 \cr \text{II} & a &+& b & & &=& 1 \end{array}