And so it's delta four, where four means that's where the bond begins. So we have a bond between carbon four and five, and that's what we mean by delta four. Now in this particular case, what exactly is the configuration, what is the stereochemistry of this bond? Well, it's a trans double bond because these two groups basically .2 opposites in the opposite side. And so what that means is it's a trans delta four. Basically to describe the stereo chemistry of the double bond, all we have to add is a CIS or trans to the beginning of that double bond.