TeX Quellcode:

\begin{array}{crcrcrcrcl} \text{I} & a &-& b &+& 4 &=& 2 &\vert& -4 \cr \text{III} & 4a &+& 2b &+& 4 &=& 12 &\vert& -4 \cr\cr \text{I} & a &-& b & & &=& -2 \cr \text{III} & 4a &+& 2b & & &=& 8 \end{array}