Coq:
relevant information to be exported
Parsing rules: proof-engine dependent
Pretty-printing rules: should depend only on
author, user choices, the available browser and so on
Tactics:
again, proof engine dependent. Moreover, they are not the real
informative content and are not at the level at which a proof must
be understood ("Auto" vs. "Obvious").
Redundant information added to speed-up elaboration:
- Useless for most purposes
- Possibly useless to other proof-checkers
- Problems of consistency: redundancy requires checks