diff --git a/src/muz/rel/udoc_relation.cpp b/src/muz/rel/udoc_relation.cpp
index 1ea185530..3e01a8ba6 100644
--- a/src/muz/rel/udoc_relation.cpp
+++ b/src/muz/rel/udoc_relation.cpp
@@ -20,40 +20,6 @@ Revision History:
 
 Notes:
 
-    Current pending items:
-    - Profile and fix bottlnecks:
-      - Potential bottleneck in projection exercised in some benchmarks.
-        Projection is asymptotically very expensive. We are here interested in 
-        handling common/cheap cases efficiently.
-      - Simplification of udoc and utbv (from negated tails) after operations such as join and union.
-      - The current simplification is between cheap and expensive. Some low-cost simplification 
-        based on sorting + coallescing and detecting empty docs could be used.
-      - There are several places where code copies a sequence of bits from one vector to another.
-        Any such places in udoc_relation should be shifted down to 'doc_manager'. Loops in 'doc_manager' 
-        should be shifted down to 'tbv_manager' and loops there should be moved to 'fixed_bitvector_manager'.
-        Finally, more efficient and general implementations of non-aligned copies are useful where such
-        bottlnecks show up on the radar.
-   - Fix filter_by_negated.
-     Current implementation seems incorrect. The fast path seems right, but the slow path does not.
-     Recall the semantics:
-      filter_by_negation(tgt, neg, columns in tgt: c1,...,cN, 
-         corresponding columns in neg: d1,...,dN):
-         tgt := {x: x\in tgt_0 && ! \exists y: ( y \in neg & pi_c1(x)= pi_d1(y) & ... & pi_cN(x)= pi_dN(y) ) }
-     We are given tgt, and neg as two udocs. 
-     The fast pass removes doc's t from tgt where we can establish 
-     that for every x in t there is a n in neg and a y in n, 
-     such that projections(x) = projections(y).
-     This is claimed to be the case if projections(n) contains projections(t).
-   
-     The slow pass uses the projection to create a doc n' from each n that has the same signature as tgt.
-     It then subtracts each n'. The way n' is created is by copying bits from n.
-     This seems wrong, for example if the projection contains overlapping regions.
-     Here is a possible corrected version:
-     define join_project(tgt, neg, c1, .., cN, d1, .. , dN) as
-           exists y : y \in neg & x in tgt & pi_c1(x)= pi_d1(y) & ... & pi_cN(x)= pi_dN(y) )
-     return tgt \ join_project(tgt, neg, c1, .., cN, d1, .. , dN)
-     We have most of the facilities required for a join project operation.
-     For example, the filter_project function uses both equalities and deleted columns.
 --*/
 #include "udoc_relation.h"
 #include "dl_relation_manager.h"
diff --git a/src/tactic/tactical.cpp b/src/tactic/tactical.cpp
index cfb4ec194..87974ea60 100644
--- a/src/tactic/tactical.cpp
+++ b/src/tactic/tactical.cpp
@@ -1229,6 +1229,9 @@ class using_params_tactical : public unary_tactical {
     params_ref m_params;
 public:
     using_params_tactical(tactic * t, params_ref const & p):unary_tactical(t), m_params(p) {
+        param_descrs r;
+        collect_param_descrs(r);
+        p.validate(r);
         t->updt_params(p);
     }
 
diff --git a/src/util/params.cpp b/src/util/params.cpp
index 7d517fb10..130b18cc9 100644
--- a/src/util/params.cpp
+++ b/src/util/params.cpp
@@ -302,10 +302,19 @@ public:
         svector<params::entry>::const_iterator end = m_entries.end();
         for (; it != end; ++it) {                                
             param_kind expected = p.get_kind(it->first);
-            if (expected == CPK_INVALID)
-                throw default_exception("unknown parameter '%s'", it->first.str().c_str());
-            if (it->second.m_kind != expected) 
-                throw default_exception("parameter kind mismatch '%s'", it->first.str().c_str());
+            if (expected == CPK_INVALID) {
+                std::stringstream strm;
+                strm << "unknown parameter '" << it->first.str() << "'\n";    
+                strm << "Legal parameters are:\n";
+                p.display(strm, 2, false, false);
+                throw default_exception(strm.str());
+            }
+            if (it->second.m_kind != expected) {
+                std::stringstream strm;
+                strm << "Parameter " << it->first.str() << " was given argument of type ";
+                strm << it->second.m_kind << ", expected " << expected;                
+                throw default_exception(strm.str());
+            }
         }
     }