Simplify x(x-1)

[Former user]

Simplify x(x-1) or x*(x-1) return x(x-1). Should return x^2-1, shouldn't it?

[Axel Kramer]

Simplify uses the LeafCount() function to "measure" which expression is "easier".

>>> LeafCount(x*(x-1))
5 

>>> LeafCount(x^2-x)
7

If you look at the FullForm of the expressions you can see that -x is represented as Times(-1, x) which has a LeafCount of 3:

>>> FullForm(x*(x-1))
"Times(x, Plus(-1, x))"

>>> FullForm(x^2-x)
"Plus(Times(-1, x), Power(x, 2))"