== Relationship between call and put delta == 

 This section is basically wrong. It contains the correct statement that long call plus short put is equivalent to a forward. But it is not the case that the delta of a forward contract equals 1. That delta actually equals the discount factor (on the risk free rate to the time of delivery). The delta of a future, which is marked to market and settled ("margined") daily, does equal 1. (The delta of a share of stock also equals 1.) But note that the fact of a future or share have a delta of 1does not imply that options on futures or stocks will have call and put deltas with a difference of 1. Because generally options are not margined / daily settled. The only options where call and put deltas have a difference of 1 are options that are margined like futures, with daily settlement of the PNL. American options on Brent crude on ICE exchange are one example. I think there is a small handful of more around the world. But generally a long option requires full payment of premium upfrontnot just variation margin. And a short option requires posting of full value of the option, plus variation margin. Futures, and options with futures style margining, only require the posting of variation margin for long and short options (which is updated on a daily basis (and reduces as the underlying moves favorably and can be immediately withdrawn to that extent)).  

 So this section is simply wrong. It uses an excess of sentences to make a very simple point. And the point is only precisely correct in rarely traded contract specs. The correct statement is that the difference of call and put deltas for the vast majority of what is traded have a difference of about 1, and to be exact have a difference of the relevant discount factor.  

 I guess I should just rewrite the whole thing, as opposed to deleting it (simplest response) or leaving it for someone else to address (another easy way out).