View Compilation Error

0_0_37730210_25998.cpp: In function 'int LCA_st_query(int, int)':
0_0_37730210_25998.cpp:42:10: error: 'f' was not declared in this scope
   if( d[ f[y][i] ] >=d[x] )
          ^
0_0_37730210_25998.cpp:47:7: error: 'f' was not declared in this scope
   if( f[x][i]!=f[y][i] )
       ^
0_0_37730210_25998.cpp:49:9: error: 'f' was not declared in this scope
  return f[x][0];
         ^