View Compilation Error

0_0_33691253_21098.cpp: In function 'void tarjan(int)':
0_0_33691253_21098.cpp:76:28: error: 'G' was not declared in this scope
     for (int i = 0; i < SZ(G[x]); i++) {
                            ^
0_0_33691253_21098.cpp:15:22: note: in definition of macro 'SZ'
 #define SZ(a) (int)((a).size())
                      ^