diff --git a/backend/cn/solver.mli b/backend/cn/solver.mli
index 8b1b034f9..18321fc84 100644
--- a/backend/cn/solver.mli
+++ b/backend/cn/solver.mli
@@ -1,7 +1,12 @@
+(* Module Solver -- Interface to the SMT solver via SMTLIB *)
+
 type solver
 type model
+(* (TODO BCP: The "with quantifiers" part will be the instantiations that the
+   solver found -- is that right?) *)
 type model_with_q = model * (Sym.t * LogicalSorts.t) list
 
+(* Global flags to pass to the solver (TODO BCP: Could use a bit more documentation, maybe) *)
 val random_seed : int ref
 val log_to_temp : bool ref
 val log_dir     : (string option) ref
@@ -9,44 +14,52 @@ val solver_path : (string option) ref
 val solver_flags : ((string list) option) ref
 val solver_type : (Simple_smt.solver_extensions option) ref
 
+(* Create a solver *)
 val make : Global.t -> solver
 
-val num_scopes : solver -> int
-val push : solver -> unit
-val pop : solver -> int -> unit
+(* Incrementally (and imperatively) add an assumption to the solver state *)
 val add_assumption : solver -> Global.t -> LogicalConstraints.t -> unit
 
-val set_slow_smt_settings : float option -> string option -> unit
-
+(* Saving and restoring solver state, to support backtracking *)
+val push : solver -> unit
+val pop : solver -> int -> unit
+(* TODO BCP: What is this? *)
+val num_scopes : solver -> int
 
+(* Run the solver.  Note that we pass the assumptions explicitly even
+   though they are also available in the solver context, because CN is
+   going some simplification on its own. *)
 val provable :
   loc:Locations.t ->
-  solver:solver ->
-  global:Global.t ->
+  solver:solver ->                    (* Current solver, from the typing context *)
+  global:Global.t ->                  (* Global typing context  (TODO BCP: ?? *) *)
   assumptions:Context.LCSet.t ->
-  simp_ctxt:Simplify.simp_ctxt ->
-  pointer_facts:IndexTerms.t list ->
+  simp_ctxt:Simplify.simp_ctxt ->     (* will go away? *)
+  pointer_facts:IndexTerms.t list ->  (* will go away? *)
   LogicalConstraints.t ->
   [> `True | `False ]
 
-
+(* Ask the solver for the model that it found in a call to [provable] *)
 val model :
   unit ->
   model_with_q
 
-
-
+(* Ask the solver to evaluate a CN term in the context of a
+   model.  (Might return None in case we ask for the value of a "don't
+   care" value in the (minimal) model.) *)
+(* TODO BCP: I don't understand how this could ever be called -- how do we get a
+   model to pass it??? *)
 val eval :
-  Global.t ->
+  Global.t ->   (* TODO BCP: IIUC Christopher thinks this is not needed? *)
   model ->
   IndexTerms.t ->
   IndexTerms.t option
 
+(* TODO BCP: What is this? *)
+val set_slow_smt_settings : float option -> string option -> unit
 
-
-
+(* Debugging *)
+(* TODO BCP: This one seems misnamed -- it doesn't return a string...? *)
 val debug_solver_to_string : solver -> unit
-
 val debug_solver_query : solver -> Global.t -> Context.LCSet.t ->
   IndexTerms.t list -> LogicalConstraints.t -> unit
-