View Compilation Error

0_0_32093733_18516.cpp: In function 'int main()':
0_0_32093733_18516.cpp:13:2: error: 'set' was not declared in this scope
  set<string>A,B;
  ^
0_0_32093733_18516.cpp:13:12: error: expected primary-expression before '>' token
  set<string>A,B;
            ^
0_0_32093733_18516.cpp:13:13: error: 'A' was not declared in this scope
  set<string>A,B;
             ^
0_0_32093733_18516.cpp:13:15: error: 'B' was not declared in this scope
  set<string>A,B;
               ^