To support better math for pdf

[Ducasse]

We could introduce a format to support $ $

and we could introduce an environment for [ and ]

[ confidence({ eggs } \Rightarrow { bacon }) = \frac{support({ eggs, bacon })}{support({ eggs })} = \frac23 ] [ confidence({ bacon } \Rightarrow { eggs }) = \frac{support({ eggs, bacon })}{support({ bacon })} = 1 ]

[Ducasse]

we should introduce

${begin=array}$ ${end=array}$ as environment

and ${math }$