[Ubuntu] Installing both Grass 6.4 and Grass 7 on Ubuntu 14.04

[Luís de Sousa]

Dear all,

I have a few old scripts depending on Grass 6.4 that I would prefer
not to migrate to Grass 7 at this stage. Ideally, I would have both
Grass 7 (for new stuff) and Grass 6.4 installed.

Would this be possible from the unstable PPA? Or is downgrading the
package the only way to get Grass 6.4.

Thank you,

Luís