My fold/reduce 'cheat sheet' is something like:
For the list (a,b,c,d) fold/reduce is:
reduceLeft(f) => f(f(f(a,b),c),d)
foldLeft(Z)(f) => f(f(f(f(Z,a),b),c),d)
("applies the function from the left")
reduceRight(f) => f(a,f(b,f(c,d)))
foldRight(Z)(f) => f(a,f(b,f(c,f(d,Z))))
("applies the function from the right")
[EDIT: as you see, fold and reduce are essentially the same, but fold starts with an outside element ]
