tag
Tag.type tag
Abstract type of oracle tags.
The type tag
is used to track the use of oracles in HOL.
An ‘oracle’ is a source of theorems that are not proved, but just
asserted. In HOL, such unproven ‘theorems’ are used to incorporate the
results of external proof tools. Each theorem coming from an oracle has
a tag attached to it. This tag gets copied to any theorems hereditarily
generated from an oracular theorem by inference.