⊦ s2i(i2s(j - j0)) = s2i(i2s(j - s2i(i2s(j0))))
⊦ s2i(i2s(j - s2i(i2s(j0)))) = s2i(i2s(s2i(i2s(j)) - s2i(i2s(j0))))
Used terms: j0, j