Are you sure it is not
In which case it is sufficient as
b-1 = b^2-1
b^2-b = 0 (add 1 to both sides and subtract b)
b can only have two values 0 or 1
If it is 0 then ab^2 will be 0.
If it is 1, then a has to be 0 as a=b^2-1 - so ab^2= 0
ab^2 is therefore 0.
Hope this helps (please recheck as I'm sure I have reviewed this before and statement 2 was as I have stated)
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