Following on from the book, how does one then optimize the paramaters 'Fast' and 'Slow'?

My attempts fail big time. After setting the Paramaters flag, I attempted to insert the optimize function for the Fast moving average like so.

vars Price = series(priceClose());
vars Fast = ptimize((1,1,20,1)series(SMA(Price,3));
vars Slow = series(SMA(Price,30));

The error message is as follows.

Luxor compiling.............
Error in 'line 23: syntax error
< vars Fast = optimize((1,1,20,1)series(SMA(Price,3));
>.