https://www.isis.vanderbilt.edu Syntheto is a surface language for carrying out formally verified program synthesis by transformational refinement in ACL2 using the APT toolkit. Syntheto aims at providing more familiarity and automation, in order to make this technology more widely usable. Syntheto is a strongly statically typed functional language that includes both executable and non-executable constructs, including facilities to state and prove theorems and facilities to apply proof-generating transformations. Syntheto is integrated into an IDE with a notebook-style, interactive interface that translates Syntheto to ACL2 definitions and APT transformation invocations, and back-translates the prover's results to Syntheto; the bidirectional translation happens behind the scenes, with the user interacting solely with Syntheto.* US Government Notice: Approved for Public Release, Distribution Unlimited 1 We are not taking a position on whether Lisp-like syntax is better or worse than Java-like syntax, or whether untyped languages are better or worse than typed languages; in fact, our position is simply that there are relative pros and cons. We are merely stating that, based on our observations, the majority of users, both inside and outside the formal methods community, finds certain language features more familiar and intuitive than others. This motivates our design choices for Syntheto.