View Compilation Error

0_0_21599027_19087.cpp: In function 'int Pop(int)':
0_0_21599027_19087.cpp:2:10: error: 'tree' was not declared in this scope
  int l = tree[x].l;
          ^
0_0_21599027_19087.cpp:5:19: error: 'Merge' was not declared in this scope
  return Merge(l, r);
                   ^