Gamma is the change of delta as a function of underlying price. So, since here we are shifting strike rather then spot, our new delta (in absence of other effects) will be original delta plus gamma contribution due to change in strike. I.e. if gamma is zero (for example, both options are DITM) your delta at new strike is same as delta at old strike.Why you have to use gamma ko × (k1-ko)? Isnt gamma the rate of change of delta?
There are all sorts of second and third order effects that I am omittingAnd what are the ... behind?
