i < 0 ⊦ i2b(i + j) = i2b(b2i(i2b(i)) + j), ¬ i < 0 ∧ ¬ j < 0
⊦ i < 0, i2b(i + j) = i2b(b2i(i2b(i)) + j), ¬ i < 0 ∧ ¬ j < 0
Used formulas: i < 0