For addition adding incrementing grading makes sense, I can't make sense out of the incrementing it for multiplication too, potential bug?

def __mul__(self, other):
other = other if isinstance(other, Value) else Value(other)
out = Value(self.data * other.data, (self, other), '*')

def _backward():
self.grad += other.data * out.grad
other.grad += self.data * out.grad
out._backward = _backward

return out

If you have an expression of type (x*y)*(x*z) then the gradient w.r.t x is not additive, right?