foo.cc: In function 'int cover(int, int)':
foo.cc:33:15: warning: left operand of comma operator has no effect [-Wunused-value]
     return zj,yj,sj,xj;
               ^~
foo.cc:33:18: warning: right operand of comma operator has no effect [-Wunused-value]
     return zj,yj,sj,xj;
                  ^~
foo.cc:33:21: warning: right operand of comma operator has no effect [-Wunused-value]
     return zj,yj,sj,xj;
                     ^~

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