diff --git a/src/math/dd/dd_pdd.h b/src/math/dd/dd_pdd.h
index 3ac44d974..0fd9606bb 100644
--- a/src/math/dd/dd_pdd.h
+++ b/src/math/dd/dd_pdd.h
@@ -9,6 +9,9 @@ Abstract:
 
     Poly DD package
 
+    It is a mild variant of ZDDs. 
+    In PDDs arithmetic is either standard or using mod 2 (over GF2).
+
     Non-leaf nodes are of the form x*hi + lo
     where 
     - maxdegree(x, lo) = 0, 
diff --git a/src/math/grobner/pdd_grobner.cpp b/src/math/grobner/pdd_grobner.cpp
index a0fa7edd4..9edc4aac9 100644
--- a/src/math/grobner/pdd_grobner.cpp
+++ b/src/math/grobner/pdd_grobner.cpp
@@ -425,7 +425,7 @@ namespace dd {
         // they watch the top most variable in poly
         i = 0;
         for (auto const& w : m_watch) {
-            for (equation const* e : w) {
+            for (equation* e : w) {
                 VERIFY(!e->poly().is_val());
                 VERIFY(e->poly().var() == i);
                 VERIFY(!e->is_processed());