In file included from /in/Compile/check.cpp:7:
/in/sokoban.hpp:211:34: error: no member named 'size' in 'Position'
        if (initial_state.player.size() != 1 || initial_state.boxes.empty() ||
            ~~~~~~~~~~~~~~~~~~~~ ^
1 error generated.
/in/Compile/Makefile:16: recipe for target 'main' failed
make: *** [main] Error 1