  Smtlink is an extension of ACL2 with Satisfiability Modulo Theories (SMT)
solvers. We presented an earlier version at ACL2'2015. Smtlink 2.0 makes major
improvements over the initial version with respect to soundness, extensibility,
ease-of-use, and the range of types and associated theory-solvers supported.
Most theorems that one would want to prove using an SMT solver must first be
translated to use only the primitive operations supported by the SMT solver --
this translation includes function expansion and type inference. Smtlink 2.0
performs this translation using a sequence of steps performed by verified
clause processors and computed hints. These steps are ensured to be sound. The
final transliteration from ACL2 to Z3's Python interface requires a trusted
clause processor. This is a great improvement in soundness and extensibility
over the original Smtlink which was implemented as a single, monolithic,
trusted clause processor. Smtlink 2.0 provides support for FTY defprod,
deflist, defalist, and defoption types by using Z3's arrays and user-defined
data types. We have identified common usage patterns and simplified the
configuration and hint information needed to use Smtlink.
