let a be Integer; :: thesis: for V being Z_Module
for v being VECTOR of V holds (- a) * (- v) = a * v
let V be Z_Module; :: thesis: for v being VECTOR of V holds (- a) * (- v) = a * v
let v be VECTOR of V; :: thesis: (- a) * (- v) = a * v
thus (- a) * (- v) = (- (- a)) * v by Th5
.= a * v ; :: thesis: verum