1. a : ℚ
2. b : ℚ
3. c : ℚ
4. c < 0
5. 0 < -(c)
⊢ uiff(a < b;c * b < c * a)
{ Auto }
6. a < b
⊢ c * b < c * a
6. c * b < c * a
⊢ a < b