/in/foo.c:49:5: error: redefinition of 'SetUnion'
 int SetUnion(int a1[], int n1, int a3[], int n3, int b[])
     ^~~~~~~~
/in/foo.c:27:5: note: previous definition of 'SetUnion' was here
 int SetUnion(int a1[], int n1, int a2[], int n2, int b[])
     ^~~~~~~~