Ruzsa’s genus-one problem

Found by exploiting the multiple-of-7 fiber structure. Starting from the size-14 witness for N=308=7*44, write each element as r+7t and compress the quotient coordinate from t mod 44 to t mod 42 while preserving r mod 7. A ceiling-type compression merges one point and leaves the valid 13-set shown here. This preserves the recurring 4+4+4+2 residue-fiber pattern up to the merged point.