remove a few default constructors

src/math/grobner/grobner.h

@@ -48,7 +48,7 @@ public:
         friend class grobner;
         friend struct monomial_lt;
 
-        monomial() {}
+        monomial() = default;
     public:
         rational const & get_coeff() const { return m_coeff; }
         unsigned get_degree() const { return m_vars.size(); }
@@ -63,7 +63,7 @@ public:
         ptr_vector<monomial> m_monomials;     //!< sorted monomials
         v_dependency *         m_dep;           //!< justification for the equality
         friend class grobner;
-        equation() {}
+        equation() = default;
     public:
         unsigned get_num_monomials() const { return m_monomials.size(); }
         monomial const * get_monomial(unsigned idx) const { return m_monomials[idx]; }

src/math/lp/explanation.h

@@ -29,7 +29,7 @@ class explanation {
     vector<std::pair<constraint_index, mpq>> m_vector;
     ci_set  m_set;   
 public:
-    explanation() {}
+    explanation() = default;
     
     template <typename T>
     explanation(const T& t) {

src/math/lp/general_matrix.h

@@ -180,7 +180,7 @@ public:
         m_column_permutation.transpose_from_left(j, k);
     }
     
-    general_matrix(){}
+    general_matrix() = default;
     general_matrix(unsigned n) :
         m_row_permutation(n),
         m_column_permutation(n),

src/math/lp/hnf_cutter.cpp

@@ -19,8 +19,7 @@ namespace lp  {
         lia(lia), 
         lra(lia.lra),
         m_settings(lia.settings()),
-        m_abs_max(zero_of_type<mpq>()),
-        m_var_register() {}
+        m_abs_max(zero_of_type<mpq>()) {}
     
     bool hnf_cutter::is_full() const {
         return

src/math/lp/implied_bound.h

@@ -44,7 +44,7 @@ class implied_bound {
             k = static_cast<lconstraint_kind>(k / 2);
         return k;
     }
-    implied_bound(){}
+    implied_bound() = default;
     implied_bound(const mpq & a,
                   unsigned j,
                   bool is_lower_bound,

src/math/lp/indexed_vector.h

@@ -76,7 +76,7 @@ public:
 
     }
 
-    indexed_vector() {}
+    indexed_vector() = default;
 
     void resize(unsigned data_size);
     unsigned data_size() const {

src/math/lp/lar_term.h

@@ -70,7 +70,7 @@ public:
         }
     }
     // constructors
-    lar_term() {}
+    lar_term() = default;
     lar_term(const vector<std::pair<mpq, unsigned>>& coeffs) {
         for (auto const& p : coeffs) {
             add_monomial(p.first, p.second);

src/math/lp/nla_tangent_lemmas.h

@@ -17,7 +17,7 @@ struct point {
     rational x;
     rational y;
     point(const rational& a, const rational& b): x(a), y(b) {}
-    point() {}
+    point() = default;
     inline point& operator*=(rational a) {
         x *= a;
         y *= a;