Bridges" or "ad-hoc" information exchange solutions: The pairs of systems in this category include bridges combining PVS, HOL, or Isabelle with Maple, NuPRL
with Weyl, Omega with Maple/GAP, Isabelle with Summit, and most recently, Lean with Mathematica [35,45-51], The example given above, bridging Isabelle and Maple, is an example of an approach from this category.
For recent notable work, I focus on some significant theorem-proving systems: the geometry theorem provers of Chou (Chou, Gao, and Zhang 1994; Chou 1988); the Boyer and Moore (1988) interactive theorem prover NQTHM and its successor ACL2 (Kaufmann and Moore 1996); the rewrite rule laboratory (RRL) of Kaput and Zhang (1995); the resolution prover OTTER (McCune and Otter 1997; McCune 1994) and the equational logic prover EQP by McCune (1996); the interactive higher-order logic provers NUPRL (Constable et al.
Lucent Technologies (Bell Laboratories) is using a combination of HOL and NUPRL tO verify the SCI cache coherency protocol.
The ability to tackle these real-world problems is primarily the result of the improved capabilities of interactive systems such as NQTHM, ACL2, PVS, NUPRL, HOL, COQ (Coquand and Huet [INRIA] 1988), and ISABELLE (Paulson [Cambridge] 1994).
However, many other systems now have user communities of their own, some sizable: NQTHM, ACL2, and RRL, for example, and the higher-order logic systems HOL, NUPRL, ISABELLE, PVS, COQ, and TPS.
The verification of the SCI cache coherency protocol mentioned earlier uses a linking of HOL and NUPRL, which allows many theorems from HOL to be imported into NUPRL.
This category may itself be subdivided into provers for a specific logic like the Boyer-Moore prover  and LCF , and generic provers such as ELF , NuPRL , and Isabelle .
NuPRL features transformation tactics to support the reuse of proofs.