Redlog is integrated with the interactive computer algebra system REDUCE. It supplements the open-source computer algebra system REDUCE with more than 100 functions on first-order formulas. Redlog has been publicly available since 1995 and is systematically being improved and developed further. The name Redlog stands for REDUCE Logic System.

Redlog generally works with interpreted first-order logic in contrast to free first-order logic. Each first-order formula in Redlog must exclusively contain atoms from one particular Redlog-supported domain, which corresponds to a choice of admissible functions and relations with fixed semantics. Redlog-supported domains include nonlinear real arithmetic (Tarski Algebra), Presburger arithmetic, parametric quantified Boolean formulas, and many more.

Redlog provides a productive interactive environment for constructing, analyzing, and manipulating formulas. This includes various normal form computations, advanced logical and algebraic simplification techniques, and quantifier elimination and decision procedures. All this can be combined with the symbolic computation power of the host computer algebra system REDUCE.

Effective quantifier elimination procedures for the various
supported theories play a central role in Redlog: Given a
first-order formula `φ`, Redlog computes an
equivalent formula `φ'` that does not contain
any quantifier. The screenshot shows an example in the real
domain.

Redlog's quantifier elimination procedures are also decision
procedures. For instance, Redlog's quantifier elimination
computes "false" for the decision
problem `∀a∃b(φ)` with `φ` as
above. Some further decision methods in Redlog are not based on
quantifier elimination.

REDUCE has been designed as an interactive computer algebra system. The REDUCE source distribution includes a C library for managing REDUCE processes and communicating with these processes. Besides communication via REDUCE command strings, e.g., an XML-based communication protocol can be easily realized.

Both REDUCE and Redlog are open-source and freely distributed under a very liberal FreeBSD License.