I'm trying to simplify an expression, which has a factor of $\lambda(\lambda-1)$, where $\lambda$ may be either $1$, or $0$. So I try:
FullSimplify[λ (λ - 1), λ == 0 || λ == 1]
But the expression doesn't simplify to $0$. I've tried changing the assumptions to
λ ∈ Integers && 0 <= λ <= 1, with the same result.
What's going on? How to convince Mathematica to do the simplification?