diff --git a/src/math/polysat/forbidden_intervals.cpp b/src/math/polysat/forbidden_intervals.cpp
index ff77db9d7..55a32a30f 100644
--- a/src/math/polysat/forbidden_intervals.cpp
+++ b/src/math/polysat/forbidden_intervals.cpp
@@ -20,10 +20,11 @@ Author:
 
 namespace polysat {
 
-    /** Precondition: all variables other than v are assigned.
+    /** 
      *
-     * \param[out] out_interval     The forbidden interval for this constraint
-     * \param[out] out_neg_cond     Negation of the side condition (the side condition is true when the forbidden interval is trivial). May be NULL if the condition is constant.
+     * \param[in] c                 Original constraint
+     * \param[in] v                 Variable that is bounded by constraint
+     * \param[out] fi               "forbidden interval" record that captures values not allowed for v
      * \returns True iff a forbidden interval exists and the output parameters were set.
      */
 
@@ -55,7 +56,7 @@ namespace polysat {
         SASSERT(b2.is_val());
 
         // TBD: use fi.coeff = -1 to tell caller to treat it as a diseq_lin.
-        // record a1, a2, b1, b2 for fast access and add side conditions on b1, b2?
+        // record a1, a2, b1, b2 for fast access, add non_unit side conditions on b1 = e1, b2 = e2?
         if (a1 != a2 && !a1.is_zero() && !a2.is_zero())
             return false;
    
@@ -224,7 +225,9 @@ namespace polysat {
     void forbidden_intervals::add_non_unit_side_conds(fi_record& fi, pdd const& b1, pdd const& e1, pdd const& b2, pdd const& e2) {
         if (fi.coeff == 1)
             return;
-        fi.side_cond.push_back(s.eq(b1, e1));
-        fi.side_cond.push_back(s.eq(b2, e2));
+        if (b1 != e1)
+            fi.side_cond.push_back(s.eq(b1, e1));
+        if (b2 != e2)
+            fi.side_cond.push_back(s.eq(b2, e2));
     }
 }
diff --git a/src/math/polysat/viable.cpp b/src/math/polysat/viable.cpp
index ae5f5274a..29dcce50e 100644
--- a/src/math/polysat/viable.cpp
+++ b/src/math/polysat/viable.cpp
@@ -178,6 +178,10 @@ namespace polysat {
         return true;
     }
 
+    bool viable::refine_viable(pvar v, rational const& val) {
+        return refine_equal_lin(v, val) && refine_disequal_lin(v, val);
+    }
+
     /**
     * Traverse all interval constraints with coefficients to check whether current value 'val' for
     * 'v' is feasible. If not, extract a (maximal) interval to block 'v' from being assigned val.
@@ -187,7 +191,7 @@ namespace polysat {
     *   be precisely the assigned values. This is to ensure that lo/hi that are computed based on lo_val 
     *   and division with coeff are valid. Is there a more relaxed scheme?
     */
-    bool viable::refine_viable(pvar v, rational const& val) {
+    bool viable::refine_equal_lin(pvar v, rational const& val) {
         auto* e = m_equal_lin[v];
         if (!e)
             return true;
@@ -268,6 +272,14 @@ namespace polysat {
         return true;
     }
 
+    bool viable::refine_disequal_lin(pvar v, rational const& val) {
+        auto* e = m_diseq_lin[v];
+        if (!e)
+            return true;
+        LOG("refine-disequal-lin is TBD");
+        return true;
+    }
+
     bool viable::has_viable(pvar v) {     
         refined:
         auto* e = m_units[v];
@@ -460,6 +472,7 @@ namespace polysat {
         while (e != first);
 
         // core.set_bailout();
+        // TODO - review this; c is true under current assignment?
         for (auto c : core) {
             if (c.bvalue(s) == l_false) {
                 core.reset();
@@ -506,6 +519,7 @@ namespace polysat {
     std::ostream& viable::display(std::ostream& out, pvar v) const {
         display(out, v, m_units[v]);
         display(out, v, m_equal_lin[v]);
+        display(out, v, m_diseq_lin[v]);
         return out;
     }
 
diff --git a/src/math/polysat/viable.h b/src/math/polysat/viable.h
index d2470c04c..feb01af25 100644
--- a/src/math/polysat/viable.h
+++ b/src/math/polysat/viable.h
@@ -50,6 +50,10 @@ namespace polysat {
 
         bool refine_viable(pvar v, rational const& val);
 
+        bool refine_equal_lin(pvar v, rational const& val);
+
+        bool refine_disequal_lin(pvar v, rational const& val);
+
         std::ostream& display(std::ostream& out, pvar v, entry* e) const;
 
         void insert(entry* e, pvar v, ptr_vector<entry>& entries, entry_kind k);
@@ -60,9 +64,9 @@ namespace polysat {
         ~viable();
 
         // declare and remove var
-        void push(unsigned) { m_units.push_back(nullptr); m_equal_lin.push_back(nullptr); }
+        void push(unsigned) { m_units.push_back(nullptr); m_equal_lin.push_back(nullptr); m_diseq_lin.push_back(nullptr); }
 
-        void pop() { m_units.pop_back(); m_equal_lin.pop_back(); }
+        void pop() { m_units.pop_back(); m_equal_lin.pop_back(); m_diseq_lin.pop_back(); }
 
         void pop_viable();