| #r mx = #r mx0, #c mx = #c mx0, c < #c mx, c0 < #c mx, 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) ⊦ count(mx[c]c, λ j. j < i) = #clean0rows(mx0, i) + count(mx0[c]c, #clean0rows(mx0, i), #r mx, λ j. j < i) |