for c in ( mr )
return
encode( coverage histogram
        over     $n x(-20:20)
        values   condense +
                        over     $px x(10:20),
                                 $py y(10:20)
                        using    c[ x($px), y($py) ]>$n - 1 and c[ x($px), y($py) ]<=$n,
        "csv" )