diff --git a/src/math/polysat/forbidden_intervals.cpp b/src/math/polysat/forbidden_intervals.cpp
index 78414ae46..c1a246215 100644
--- a/src/math/polysat/forbidden_intervals.cpp
+++ b/src/math/polysat/forbidden_intervals.cpp
@@ -200,12 +200,12 @@ namespace polysat {
         if (a1 != a2 && !a1.is_zero() && !a2.is_zero())
             return false;
         SASSERT(b1.is_val());
-        SASSERT(b2.is_val());
-
-        LOG("values " << a1 << " " << a2);       
+        SASSERT(b2.is_val());    
 
         _backtrack.released = true;
 
+        // LOG("add " << c << " " << a1 << " " << b1 << " " << a2 << " " << b2);
+
         if (match_linear1(c, a1, b1, e1, a2, b2, e2, out_interval, out_side_cond))
             return true;
         if (match_linear2(c, a1, b1, e1, a2, b2, e2, out_interval, out_side_cond))
diff --git a/src/math/polysat/solver.h b/src/math/polysat/solver.h
index 74a39e5ed..784fc6601 100644
--- a/src/math/polysat/solver.h
+++ b/src/math/polysat/solver.h
@@ -66,6 +66,7 @@ namespace polysat {
         friend class ex_polynomial_superposition;
         friend class inf_saturate;
         friend class constraint_manager;
+        friend class scoped_solverv;
 
         reslimit&                m_lim;
         params_ref               m_params;
diff --git a/src/math/polysat/viable2.cpp b/src/math/polysat/viable2.cpp
index 011a9b068..67d7b853b 100644
--- a/src/math/polysat/viable2.cpp
+++ b/src/math/polysat/viable2.cpp
@@ -85,6 +85,8 @@ namespace polysat {
             e->remove_from(m_viable[v], e);
         };
 
+        //LOG("intersect " << ne->interval);
+
         if (!e) 
             m_viable[v] = create_entry();
         else {
@@ -107,6 +109,10 @@ namespace polysat {
                 }             
                 SASSERT(e->interval.lo_val() != ne->interval.lo_val());
                 if (e->interval.lo_val() > ne->interval.lo_val()) {
+                    if (first->prev()->interval.contains(ne->interval)) {
+                        m_alloc.push_back(ne);
+                        return;
+                    }
                     e->insert_before(create_entry());
                     if (e == first)
                         m_viable[v] = e->prev();
@@ -155,7 +161,7 @@ namespace polysat {
         for (; e != last; e = e->next()) {        
             if (e->interval.currently_contains(val))
                 return false;
-            if (e->interval.lo_val() < val)
+            if (val < e->interval.lo_val())
                 return true;
         }         
         return true; 
@@ -294,11 +300,13 @@ namespace polysat {
         while (true) {
             if (e->interval.is_full())
                 return e->next() == e;
-            if (e->interval.is_currently_empty())
+            if (e->interval.is_currently_empty()) 
                 return false;
+            
             auto* n = e->next();
-            if (n != e && e->interval.contains(n->interval))
+            if (n != e && e->interval.contains(n->interval)) 
                 return false;
+            
             if (n == first)
                 break;            
             if (e->interval.lo_val() >= n->interval.lo_val())
diff --git a/src/test/viable.cpp b/src/test/viable.cpp
index c3368b3dd..352f0c76f 100644
--- a/src/test/viable.cpp
+++ b/src/test/viable.cpp
@@ -8,9 +8,24 @@ namespace polysat {
         reslimit lim;
     };
 
-    struct scoped_solverv : public solver_scopev, public solver {
+    class scoped_solverv : public solver_scopev, public solver {
+    public:
         viable2 v;
         scoped_solverv(): solver(lim), v(*this) {}
+        ~scoped_solverv() {
+            for (unsigned i = m_trail.size(); i-- > 0;) {
+                switch (m_trail[i]) {
+                case trail_instr_t::viable_add_i: 
+                    v.pop_viable();
+                    break;                
+                case trail_instr_t::viable_rem_i: 
+                    v.push_viable();
+                    break;
+                default:
+                    break;
+                }
+            }
+        }
     };
 
     static void test1() {
@@ -37,8 +52,66 @@ namespace polysat {
         std::cout << s.v.find_viable(xv, val) << " " << val << "\n";      
     }
 
-    static void test2() {
+    static void add_interval(scoped_solverv& s, pvar xv, pdd x, unsigned lo, unsigned len) {
+        if (lo == 0)
+            s.v.intersect(xv, s.ule(x, len - 1));
+        else if (lo + len == 8)
+            s.v.intersect(xv, s.ule(lo, x));
+        else 
+            s.v.intersect(xv, ~s.ule(x - ((lo + len)%8), x - lo));                        
+    }
 
+    static bool member(unsigned i, unsigned lo, unsigned len) {
+        return (lo <= i && i < lo + len) ||
+            (lo + len >= 8 && i < ((lo + len) % 8));
+    }
+
+    static bool member(unsigned i, vector<std::pair<unsigned, unsigned>> const& intervals) {
+        for (auto [lo, len] : intervals)
+            if (!member(i, lo, len))
+                return false;
+        return true;
+    }
+
+    static void validate_intervals(scoped_solverv& s, pvar xv, vector<std::pair<unsigned, unsigned>> const& intervals) {
+        for (unsigned i = 0; i < 8; ++i) {
+            bool mem1 = member(i, intervals);
+            bool mem2 = s.v.is_viable(xv, rational(i));
+            if (mem1 != mem2)
+                std::cout << "test violation: " << i << " member of all intervals " << mem1 << " viable: " << mem2 << "\n";
+            SASSERT(mem1 == mem2);
+        }
+    }
+
+    static void test_intervals(vector<std::pair<unsigned, unsigned>> const& intervals) {
+        scoped_solverv s;
+        auto xv = s.add_var(3);
+        auto x = s.var(xv);
+        s.v.push(3);
+        for (auto const& [lo, len] : intervals)
+            add_interval(s, xv, x, lo, len);
+        std::cout << intervals << "\n";
+        //std::cout << s.v << "\n";
+        validate_intervals(s, xv, intervals);
+    }
+
+    static void test_intervals(unsigned count, vector<std::pair<unsigned, unsigned>>& intervals) {
+        if (count == 0) {
+            test_intervals(intervals);
+            return;
+        }
+        for (unsigned lo1 = 0; lo1 < 8; ++lo1) {
+            for (unsigned len1 = 1; len1 <= 8; ++len1) {
+                intervals.push_back(std::make_pair(lo1, len1));
+                test_intervals(count - 1, intervals);
+                intervals.pop_back();
+            }
+        }
+    }
+
+    static void test2() {
+        vector<std::pair<unsigned, unsigned>> intervals;
+        test_intervals(3, intervals);
     }
 }