if F is strictly montone increasing function F:[0,1] such that F(0)=0 and F(1)=1 and satisfies jensens equation at x=0 and at x=1
ie the restricted form where F([1+x])=F(1)/2+F(x)/2
and F(x/2)=F(0)/2+F(x)/2
jensen's equality with y=0 using F(0)=0, F(1/2^nx)=1/2^nF(x) forall non-negative n, (doubling halving,quartering etc)
and jensen at one one, F(1)=1, F([1+x]/2=1/2+F(x)/2
I presume such functions will be effectively dyadic-ally linear, and given strict monotonic increasing will be linear (or will be if continuity has to be presumed)
I
and