Hamilton's equations for double pendulum

At the bottom of the following web site are the 4 equations that I am using for a double pendulum simulation.

http://scienceworld.wolfram.com/phys...ePendulum.html

The equation for C2 has the variables P1 and P2 and I can't work out what they are.:confused:

Is it a typo and they are meant to be Pθ1 and Pθ2?

Any help would be much appreciated.