| #r mx = #r mx0, #c mx = #c mx0, c0 < #c mx, srowsorted(mx0, #r mx0, mx0), colsorted(mx0, #c mx, mx), ∀ c. c < #c mx → count(mx[c]c, λ j. j < i) ≤ count(mx[c0]c, λ j. j < i) ⊦ #clean0rows(mx, i) ≥ #clean0rows(mx0, i) + min (countevn(mx0[c0]c, #clean0rows(mx0, i), #r mx, λ j. j < i), countodd(mx0[c0]c, #clean0rows(mx0, i), #r mx, λ j. j < i)) |