Reaction mechanism of a terminal alkene with an anhydride In a reaction (as given in my textbook),

$$\ce{R-CH=CH2 + (CH3-CO)2O  -&gt; R-CH2=CH-COCH3}$$

an alkene reacts with acetic anhydride to give methyl alkenyl ketone.

I am not sure of how this proceeds, a search on google displays no links to any relevant matter, and I have not successfully found this reaction in any of the other books I possess. 

According to me, it should have been an addition reaction (characteristic of alkenes) across the double bond. But this isn't the case here. So, what exactly is the reaction mechanism?
This is the  Friedel-Crafts acylation reaction of alkene. Catalyzed by Lewis acid. Addition-elimination mechanism.