\begin{align}\braks{S(P,c,f,G)-S(Q,d,f,G)}_{H }&\leq \braks{S(P,c,f,G)-S(R,e,f,G)+S(R,e,f,G)-S(Q,d,f,G)}_{H }\\&\leq 2\cd \SUP{x,y\in[a,b],\abs{x-y}<\max \curl{\s(P),\s(Q)}}\braks{f(x)-f(y)}_{E }\cd \braks{G}_{\text{var},F}\tag{5.1}\end{align}