foo.cc: In function 'int main()':
foo.cc:22:28: error: 'greater' was not declared in this scope
   22 |     sort(a + 1, a + 1 + n, greater<int>);
      |                            ^~~~~~~
foo.cc:22:36: error: expected primary-expression before 'int'
   22 |     sort(a + 1, a + 1 + n, greater<int>);
      |                                    ^~~
foo.cc:26:8: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
   26 |     if (!(n & 1))
      |        ^

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