Sat Aug 15 11:47:05 CEST 2009

Linear pairs

It's probably better to use a different data type for linear pairs.
That way nonlinear pairs can be used as constants too.

Otoh: reusing the same pair structure allows primitives to be reused.
Even those that do cons. (Cons could be part of a shared object).

It's really not such a hurdle to manage the border between linear and
graph memory, so let's stick to the simple implementation: cons lists
are cons lists, they just have only a single reference in the linear