View Compilation Error

0_0_23500471_1723.cpp: In function 'int main()':
0_0_23500471_1723.cpp:81:9: error: reference to 'rank' is ambiguous
     pos=rank(j); split(root_r,pos,x,y); split(y,1,z,y); root_r=merge(x,y);
         ^
0_0_23500471_1723.cpp:39:5: note: candidates are: int rank(int)
 int rank(int o) {
     ^
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/move.h:57:0,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/bits/stl_pair.h:59,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/utility:70,
                 from GCC4.9.2/x86_64-w64-mingw32/include/c++/algorithm:60,
                 from 0_0_23500471_1723.cpp:2:
GCC4.9.2/x86_64-w64-mingw32/include/c++/type_traits:1340:12: note:                 template<class> struct std::rank
     struct rank
            ^