diff --git a/datalog.opam b/datalog.opam
new file mode 100644
index 0000000..d9cd7db
--- /dev/null
+++ b/datalog.opam
@@ -0,0 +1,8 @@
+opam-version: "1.2"
+name: "datalog"
+version: "0.3"
+maintainer: "Robert Atkey <bob.atkey@gmail.com>"
+authors: "Robert Atkey <bob.atkey@gmail.com>"
+license: "MIT"
+build: [["jbuilder" "build" "-p" name "-j" jobs "@install"]]
+available: [ ocaml-version >= "4.04.0" ]
diff --git a/datalog/jbuild b/datalog/jbuild
index 94b5a62..a257bd6 100644
--- a/datalog/jbuild
+++ b/datalog/jbuild
@@ -2,4 +2,5 @@
 
 (library
  ((name datalog)
+  (public_name datalog)
   (libraries (ocamlgraph fmt))))
\ No newline at end of file
diff --git a/datalog/ruleset.ml b/datalog/ruleset.ml
index a2afca6..f014380 100644
--- a/datalog/ruleset.ml
+++ b/datalog/ruleset.ml
@@ -142,15 +142,11 @@ module Builder = struct
     | [] ->
        Ok ()
     | Atom {pred;args} :: atoms ->
-(*       match PredicateNameMap.find pred pred_info with
-         | exception Not_found ->
-            Error (Undeclared_predicate pred)
-         | {arity} ->*)
-            let used_arity = List.length args in
-            if pred.arity <> used_arity then
-              Error (Arity_mismatch { pred; used_arity })
-            else
-              check_atoms pred_info atoms
+       let used_arity = List.length args in
+       if pred.arity <> used_arity then
+         Error (Arity_mismatch { pred; used_arity })
+       else
+         check_atoms pred_info atoms
 
   let add_rule ({pred;args;rhs} as rule) t =
     match check_atoms t.predicates_so_far rhs with
diff --git a/datalog/ruleset.mli b/datalog/ruleset.mli
index 808d28c..9183d9f 100644
--- a/datalog/ruleset.mli
+++ b/datalog/ruleset.mli
@@ -1,3 +1,5 @@
+(** Datalog programs as sets of rulesets. *)
+
 type predicate_name =
   { ident : string
   ; arity : int