There appears to by a typo in one of the lines.

The line

6 * (if 3 == 0 then 1 else 1 * (YF)(1–1))

The previous line is 6 * (λx.(if x == 0 then 1 else x * (YF)(x–1)) 1) When replacing the x s with 1s, it replaces one of the x s with 1, but replaces the first one with 3.

My guess was that this was copied from the first version, and they just forgot to change one of the threes to a 1.

(that is, unless I misunderstood something, which is of course possible)

I think the line should be

6 * (if 1 == 0 then 1 else 1 * (YF)(1–1))