Math & Science ⇒ Equiation making problem

[Galmadeus]

Dear All!

I'm new to LaTeX, but i have to use it for my master thesis. My code is:

Code: Select all

\begin{equation} 
 \PP({cancer})= 1-(1- \sum_{i=1}^{6} p_i F_i (t_1,t_2))^\alfa
\end{equation}

But i always get an error message:
! Undefined control sequence.
l.658 ...- \sum_{i=1}^{6} p_i F_i (t_1,t_2))^\alfa

?

What do i do wrong? (\PP is a big probability P)

[Johannes_B]

Maybe \alpha?