Don't expand(product(f(i),i=M+1..N+1)) to f(N+1)*(product(f(i),i=M+1..N)) either
Don't expand(product(f(i),i=M+1..N+1)) to f(N+1)*(product(f(i),i=M+1..N)) either

because what if M=N+1?

zachsully/hakaru,zaxtax/hakaru,zaxtax/hakaru,zachsully/hakaru