Hi Felix,

Many of your questions have been well answered already by Petros and
Mark, but here are some comments on two items:

| 2) Where are definitions stored, anyway? There seems to be some global
| state involved. Is there a way to make definitions locally? Or to pass
| definitions around explicitly?

At the moment, the definitions are just stored in a mutable list, as you
say. The actual variable (see "the_definitions" in fusion.ml) is buried
in the logical kernel but you can inspect it by "definitions()", and of
course it gets extended when you make a definition.

In some ways it would be more elegant to remove such uses of mutable
state, which can probably be done without significantly compromising
simplicity or efficiency. See for example Freek Wiedijk's "Stateless HOL"
paper:

  http://arxiv.org/abs/1103.3322v1

| 3) HOL Light has large libraries for num, int and real. Are there also
| libraries for abstract groups, rings or fields?

Not in the standard distribution, anyway, though some people may well
have developed their own. Generally the mathematical theories included
in the core distribution are biased towards specific structures rather
than general axiomatic theories.

John.

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