View Compilation Error

0_0_36376614_11447.cpp: In function 'void merge(const V&, const V&, V&)':
0_0_36376614_11447.cpp:23:46: error: 'ext' was not declared in this scope
   ext(A[i].first < B[i].first ? A[i++]:B[j++]);
                                              ^
0_0_36376614_11447.cpp:26:13: error: 'ext' was not declared in this scope
   ext(A[i++]);
             ^
0_0_36376614_11447.cpp:29:13: error: 'ext' was not declared in this scope
   ext(B[j++]);
             ^