Andres,

Your code should be like so:

^self class new: value + (self negated and: [aProbablity negated]) value


The reason is is that the 'and:' msg is a keyword msg that takes a block 
of code as an argument. Its' declaration will be like so: 

and: aBlock

< code here >


Look at the implementors of 'and:' and you'll see what I mean....

Hope this helps,

Sam Griffith Jr.
staypufed at aol.com
staypufd at gte.net