diff --git a/cpp/src/board.cpp b/cpp/src/board.cpp
index ae39018..1dfa233 100644
--- a/cpp/src/board.cpp
+++ b/cpp/src/board.cpp
@@ -1,7 +1,11 @@
 #include "board.hpp"
 
+#include "pieces/piece.hpp"
+
+#include <algorithm>
 #include <cctype>
 #include <map>
+#include <stdexcept>
 
 Board Board::setup_fen_position(std::string fen) {
     Board board;
@@ -37,7 +41,7 @@ Board Board::setup_fen_position(std::string fen) {
     return board;
 }
 
-std::string Board::to_fen() {
+std::string Board::to_fen() const {
     std::map<int, char> p2c{
         {Piece::King, 'k'},
         {Piece::Pawn, 'p'},
@@ -76,7 +80,7 @@ std::string Board::to_fen() {
     return ret;
 }
 
-Board Board::make_move(Move move) {
+Board Board::make_move(Move move) const {
     int8_t dest_piece = this->squares[move.target_square];
 
     Board ret;
@@ -96,3 +100,33 @@ Board Board::make_move(Move move) {
         ret.squares[move.target_square - 8] = Piece::None;
     return ret;
 }
+
+int8_t Board::get_king_of(int8_t colour) const {
+    for (int i = 0; i < 64; i++)
+        if (this->squares[i] == (colour | Piece::King))
+            return i;
+    throw std::domain_error(
+        "Apparently there no kings of the such color in this board"
+    );
+}
+
+std::vector<int8_t> to_target_square(std::vector<Move> moves) {
+    std::vector<int8_t> ret;
+    for (Move move : moves)
+        ret.push_back(move.target_square);
+    return ret;
+}
+
+bool Board::is_check_for(int8_t colour) const {
+    int8_t king_idx = this->get_king_of(colour);
+    for (int i = 0; i < 64; i++) {
+        if (this->squares[i] == Piece::None)
+            continue;
+        std::vector<Move> moves =
+            legal_moves(this->squares[i], *this, Coords::from_index(i), true);
+        std::vector<int8_t> targets = to_target_square(moves);
+        if (std::find(targets.begin(), targets.end(), i) != targets.end())
+            return true;
+    }
+    return false;
+}
diff --git a/cpp/src/board.hpp b/cpp/src/board.hpp
index a239783..0936109 100644
--- a/cpp/src/board.hpp
+++ b/cpp/src/board.hpp
@@ -17,12 +17,18 @@ struct Coords {
 };
 
 struct Board {
+  private:
+    int8_t get_king_of(int8_t colour) const;
+
+  public:
     int8_t squares[64] = {Piece::None};
     bool white_to_play;
     int8_t w_castle_rights;
     int8_t b_castle_rights;
+
     static Board setup_fen_position(std::string fen);
 
-    Board make_move(Move);
-    std::string to_fen();
+    Board make_move(Move) const;
+    std::string to_fen() const;
+    bool is_check_for(int8_t) const;
 };
diff --git a/cpp/src/pieces/piece.cpp b/cpp/src/pieces/piece.cpp
index 9138015..b849c1d 100644
--- a/cpp/src/pieces/piece.cpp
+++ b/cpp/src/pieces/piece.cpp
@@ -2,11 +2,23 @@
 
 #include "../board.hpp"
 
+std::vector<Move>
+keep_only_blocking(const std::vector<Move> candidates, const Board& board) {
+    if (candidates.size() == 0)
+        return {};
+
+    int8_t my_colour = board.squares[candidates[0].source_square] & 0b11000;
+    std::vector<Move> ret;
+    for (Move move : candidates) {
+        Board board_after_move = board.make_move(move);
+        if (!board_after_move.is_check_for(my_colour))
+            ret.push_back(move);
+    }
+    return ret;
+}
+
 std::vector<Move> legal_moves(
-    const Piece p,
-    const Board& b,
-    const Coords xy,
-    bool looking_for_check = false
+    int8_t p, const Board& b, const Coords xy, bool looking_for_check = false
 ) {
     std::vector<Move> ret;
     switch (p) {
diff --git a/cpp/src/pieces/piece.hpp b/cpp/src/pieces/piece.hpp
index 121335d..dd1a46c 100644
--- a/cpp/src/pieces/piece.hpp
+++ b/cpp/src/pieces/piece.hpp
@@ -23,7 +23,8 @@ enum Colour : int8_t {
 class Board;
 struct Coords;
 
-std::vector<Move> legal_moves(const Piece, const Board&, const Coords, bool);
+std::vector<Move> legal_moves(int8_t, const Board&, const Coords, bool);
+std::vector<Move> keep_only_blocking(const std::vector<Move>, const Board&);
 
 std::vector<Move> pawn_moves(const Board&, const Coords);
 std::vector<Move> rook_moves(const Board&, const Coords);