  Recently, our work regarding the definition of oscillating neutrino states in
Eur. Phys. J. C 80: 68 (2020), arxiv:1902.01232 [hep-ph] has been commented
upon in arXiv:2004.04739 [hep-ph]. In this note we show that, contrary to the
claim in the comment, our above-mentioned work cannot be reproduced in the
scheme of the so-called flavour Fock space approach described in the comment.
Moreover, we prove explicitly that a flavour Fock space cannot exist in a model
with massive mixed neutrinos. If the flavour Fock space scheme were viable, it
would necessarily lead, as a consequence of Coleman's theorem, to the flavour
number invariance of the Hamiltonian of mixed neutrino fields, while the
Hamiltonian is by construction flavour number violating. Quod est absurdum.
