Why did a lot of the Messerschmitt concept/1946 planes have the prefix P. as in the Me P.1109?

[Enceladus828]

I was watching this video today about oblique winged planes which reminded me of a concept/1946 German plane, the Me P.1109 which had an oblique wing design. As a kid I was pretty fascinated with these concept German planes but now I wonder why a number of the concept/1946 Messerschmitt planes had the prefix P. as in P.1101, P.1109, was P. the German equivalent of Y as in the YB-49 or was this just an unofficial name until an official name could be determined?

[CountZero]

From recent leaked panama documents it seams like :

 

P. = Paper

 

Y = You wish 

[Heliopause]

P for project I think