foo.c:39:5: error: redefinition of 'main'
   39 | int main()
      |     ^~~~
foo.c:27:5: note: previous definition of 'main' with type 'int()'
   27 | int main()
      |     ^~~~
foo.c: In function 'main':
foo.c:43:5: warning: implicit declaration of function 'xm' [-Wimplicit-function-declaration]
   43 |     xm(n,k);
      |     ^~

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