for f1, f2, f3, g1, g2, g3 being PartFunc of REAL,REAL
for t0 being Real st f1 is_differentiable_in t0 & f2 is_differentiable_in t0 & f3 is_differentiable_in t0 & g1 is_differentiable_in t0 & g2 is_differentiable_in t0 & g3 is_differentiable_in t0 holds
VFuncdiff ((f1 + g1),(f2 + g2),(f3 + g3),t0) = (VFuncdiff (f1,f2,f3,t0)) + (VFuncdiff (g1,g2,g3,t0))