diff --git a/dlx/include/dlx.hpp b/dlx/include/dlx.hpp
index 24876a2..15c81e0 100644
--- a/dlx/include/dlx.hpp
+++ b/dlx/include/dlx.hpp
@@ -7,7 +7,7 @@
 
 namespace dlx {
 
-class Dlx {
+class Dlx final {
 
   struct Cell {
     Cell *U, *D, *L, *R;
@@ -17,42 +17,18 @@ class Dlx {
       std::size_t s;
     };
 
-    auto LR_self() -> void { L = R = this; }
-    auto UD_self() -> void { U = D = this; }
-    auto LR_delete() -> void { L->R = R; R->L = L; }
-    auto UD_delete() -> void { U->D = D; D->U = U; }
-    auto UD_restore() -> void { U->D = D->U = this; }
-    auto LR_restore() -> void { L->R = R->L = this; }
-    auto LR_insert(Cell* k) -> void { L = k->L; R = k; k->L = k->L->R = this; }
-    auto UD_insert(Cell* k) -> void { U = k->U, D = k, k->U = k->U->D = this; }
-
-    static Cell* ColNew() {
-      auto c = new Cell;
-      c->UD_self();
-      c->s = 0;
-      return c;
-    }
-
-    auto CoverCol() -> void {
-      LR_delete();
-      for (auto i = D; i != this; i = i->D) {
-        for (auto j = i->R; j != i; j = j->R) {
-          j->UD_delete();
-          j->c->s--;
-        }
-      }
-    }
-
-    auto UncoverCol() -> void {
-      for (auto i = U; i != this; i = i->U) {
-        for (auto j = i->L; j != i; j = j->L) {
-          j->c->s++;
-          j->UD_restore();
-        }
-      }
-      LR_restore();
-    }
-
+    auto LR_self() -> void;
+    auto UD_self() -> void;
+    auto LR_delete() -> void;
+    auto UD_delete() -> void;
+    auto UD_restore() -> void;
+    auto LR_restore() -> void;
+    auto LR_insert(Cell* k) -> void;
+    auto UD_insert(Cell* k) -> void;
+    auto CoverCol() -> void;
+    auto UncoverCol() -> void;
+    auto ColAdd(std::size_t row_id) -> Cell*;
+    static Cell* ColNew();
   };
 
   std::vector<Cell*> ctab_;
@@ -68,6 +44,12 @@ public:
   Dlx();
   ~Dlx();
 
+  Dlx(Dlx const&) = delete;
+  auto operator=(Dlx const&) -> Dlx& = delete;
+
+  Dlx(Dlx &&);
+  auto operator=(Dlx &&) -> Dlx&;
+
   // Returns number of rows.
   auto Rows() const -> std::size_t;
 
@@ -82,14 +64,14 @@ public:
 // but it still must respect the constraints it entails.
   auto MarkOptional(std::size_t col) -> void;
 
-  // Removes a row from consideration. Returns 0 on success, -1 otherwise.
+  // Removes a row from consideration.
   // Should only be called after all dlx_set() calls.
-  auto RemoveRow(std::size_t row) -> int;
+  auto RemoveRow(std::size_t row) -> void;
 
-  // Picks a row to be part of the solution. Returns 0 on success, -1 otherwise.
-  // Should only be called after all dlx_set() calls and dlx_remove_row() calls.
+  // Picks a row to be part of the solution.
+  // Should only be called after all Set() calls and RemoveRows() calls.
   // TODO: Check the row can be legally chosen.
-  auto PickRow(std::size_t row) -> int;
+  auto PickRow(std::size_t row) -> void;
 
   auto Solve(
     std::function<void(std::size_t, std::size_t, std::size_t)> try_cb,
diff --git a/dlx/src/dlx.cpp b/dlx/src/dlx.cpp
index 651afcd..a764eda 100644
--- a/dlx/src/dlx.cpp
+++ b/dlx/src/dlx.cpp
@@ -4,11 +4,56 @@
 
 #include <limits>
 
-using namespace dlx;
+namespace dlx {
+
+auto Dlx::Cell::LR_self() -> void { L = R = this; }
+auto Dlx::Cell::UD_self() -> void { U = D = this; }
+auto Dlx::Cell::LR_delete() -> void { L->R = R; R->L = L; }
+auto Dlx::Cell::UD_delete() -> void { U->D = D; D->U = U; }
+auto Dlx::Cell::UD_restore() -> void { U->D = D->U = this; }
+auto Dlx::Cell::LR_restore() -> void { L->R = R->L = this; }
+auto Dlx::Cell::LR_insert(Cell* k) -> void { L = k->L; R = k; k->L = k->L->R = this; }
+auto Dlx::Cell::UD_insert(Cell* k) -> void { U = k->U, D = k, k->U = k->U->D = this; }
+
+auto Dlx::Cell::ColNew() -> Dlx::Cell*
+{
+  auto c = new Cell;
+  c->UD_self();
+  c->s = 0;
+  return c;
+}
+
+auto Dlx::Cell::ColAdd(std::size_t row_id) -> Cell*
+{
+  auto n = new Cell;
+  n->n = row_id;
+  n->c = this;
+  this->s++;
+  n->UD_insert(this);
+  return n;
+}
+
+auto Dlx::Cell::CoverCol() -> void {
+  LR_delete();
+  for (auto i = D; i != this; i = i->D) {
+    for (auto j = i->R; j != i; j = j->R) {
+      j->UD_delete();
+      j->c->s--;
+    }
+  }
+}
+
+auto Dlx::Cell::UncoverCol() -> void {
+  for (auto i = U; i != this; i = i->U) {
+    for (auto j = i->L; j != i; j = j->L) {
+      j->c->s++;
+      j->UD_restore();
+    }
+  }
+  LR_restore();
+}
 
-#define F(i,n) for(int i = 0; i < n; i++)
 
-#define C(i,n,dir) for(cell_ptr i = (n)->dir; i != n; i = i->dir)
 
 Dlx::Dlx() {
   root_ = Cell::ColNew();
@@ -32,28 +77,39 @@ Dlx::~Dlx() {
   delete root_;
 }
 
+Dlx::Dlx(Dlx && dlx) : ctab_{}, rtab_{}, root_{}
+{
+  std::swap(ctab_, dlx.ctab_);
+  std::swap(rtab_, dlx.rtab_);
+  std::swap(root_, dlx.root_);
+}
+
+auto Dlx::operator=(Dlx && dlx) -> Dlx& {
+  if (this != &dlx) {
+    this->~Dlx();
+    new (this) Dlx(std::move(dlx));
+  }
+  return *this;
+}
+
 auto Dlx::Rows() const -> std::size_t { return rtab_.size(); }
 auto Dlx::Cols() const -> std::size_t { return ctab_.size(); }
 
-auto Dlx::AddCol() -> void {
-  auto c = Cell::ColNew();
-  c->LR_insert(root_);
-  c->n = Cols();
-  ctab_.push_back(c);
-}
-
-auto Dlx::AddRow() -> void {
-  rtab_.push_back(nullptr);
-}
 auto Dlx::AllocCol(std::size_t n) -> void {
-  while(Cols() <= n) AddCol();
+  while(Cols() <= n) {
+    auto c = Cell::ColNew();
+    c->LR_insert(root_);
+    c->n = Cols();
+    ctab_.push_back(c);
+  }
 }
 
 auto Dlx::AllocRow(std::size_t n) -> void {
-  while(Rows() <= n) AddRow();
+  while (Rows() <= n) {
+    rtab_.push_back(nullptr);
+  }
 }
 
-
 auto Dlx::MarkOptional(std::size_t col) -> void {
   AllocCol(col);
   auto c = ctab_[col];
@@ -64,29 +120,13 @@ auto Dlx::MarkOptional(std::size_t col) -> void {
 
 
 auto Dlx::Set(std::size_t row, std::size_t col) -> void {
-  // We don't bother sorting. DLX works fine with jumbled rows and columns.
-  // We just have to watch out for duplicates. (Actually, I think the DLX code
-  // works even with duplicates, though it would be inefficient.)
-  //
-  // For a given column, the UD list is ordered in the order that dlx_set()
-  // is called, not by row number. Similarly for a given row and its LR list.
   AllocRow(row);
   AllocCol(col);
-  auto c = ctab_[col];
-
-  auto const new1 = [&]() -> Cell* {
-    auto n = new Cell;
-    n->n = row;
-    n->c = c;
-    c->s++;
-    n->UD_insert(c);
-    return n;
-  };
-  
+  auto c = ctab_[col];  
   auto & r = rtab_[row];
   
   if (!r) {
-    r = new1();
+    r = c->ColAdd(row);
     r->LR_self();
     return;
   }
@@ -99,32 +139,28 @@ auto Dlx::Set(std::size_t row, std::size_t col) -> void {
   }
 
   // Otherwise insert at end of LR list.
-  new1()->LR_insert(r);
+  c->ColAdd(row)->LR_insert(r);
 }
 
-auto Dlx::PickRow(std::size_t i) -> int {
-  auto r = rtab_.at(i);
-  if (!r) return 0;  // Empty row.
-  r->c->CoverCol();
-  for (auto j = r->R; j != r; j = j->R) {
-    j->c->CoverCol();
+auto Dlx::PickRow(std::size_t i) -> void {
+  if (auto r = rtab_.at(i)) {
+    r->c->CoverCol();
+    for (auto j = r->R; j != r; j = j->R) {
+      j->c->CoverCol();
+    }
   }
-
-  return 0;
 }
 
-
-auto Dlx::RemoveRow(std::size_t i) -> int {
-  auto & r = rtab_.at(i);
-  if (!r) return 0;  // Empty row.
-  r->UD_delete();
-  r->c->s--;
-  for (auto j = r->R; j != r; j = j->R) {
-    j->UD_delete();
-    j->c->s--;
+auto Dlx::RemoveRow(std::size_t i) -> void {
+  if (auto & r = rtab_.at(i)) {
+    r->UD_delete();
+    r->c->s--;
+    for (auto j = r->R; j != r; j = j->R) {
+      j->UD_delete();
+      j->c->s--;
+    }
+    r = nullptr;
   }
-  r = nullptr;
-  return 0;
 }
 
 auto Dlx::Solve(
@@ -140,17 +176,17 @@ auto Dlx::Solve(
       return;
     }
 
-    auto s = std::numeric_limits<std::size_t>::max();  // S-heuristic: choose first most-constrained column.
+    auto s = std::numeric_limits<std::size_t>::max();
     for (auto i = root_->R; i != root_; i = i->R) {
       if (i->s < s) {
         s = (c = i)->s;
+        
+        if (s == 0) {
+          stuck_cb(c->n);
+          return;
+        }
       }
     }
-    
-    if (!s) {
-      stuck_cb(c->n);
-      return;
-    }
 
     c->CoverCol();
     for (auto r = c->D; r != c; r = r->D) {
@@ -168,3 +204,5 @@ auto Dlx::Solve(
   };
   recurse(recurse);
 }
+
+} // namespace
\ No newline at end of file