eq { hop { filter_eq { all_rows ; class ; a - 4 } ; quantity made } ; hop { filter_eq { all_rows ; class ; a - 3 } ; quantity made } } = true
select the rows whose class record fuzzily matches to a  4 . take the quantity made record of this row . select the rows whose class record fuzzily matches to a  3 . take the quantity made record of this row . the first record is equal to the second record .