Autograd Incorrect add and mul in Golang

autograd_add_mul.go

func (v *Value) add(v1 *Value) *Value {
  nv := newValue(v.data+v1.data, nil /* incorrect, should be []*Value{v, v1} */)
  nv.backward = func() {
    v.grad = /* incorrect, should be += */ nv.grad
    v1.grad = /* incorrect, should be += */ nv.grad
  }
  return nv
}

func (v *Value) mul(v1 *Value) *Value {
  nv := newValue(v.data*v1.data, nil /* incorrect, should be []*Value{v, v1} */)
  nv.backward = func() {
    v.grad = /* incorrect, should be += */ v1.data * nv.grad 
    v1.grad = /* incorrect, should be += */ v.data * nv.grad
  }
  return nv
}