Lecture I: The neutrino triple
Neutrinos existence
Are there different neutrinos, how many?
Neutrinos number and cosmology

Lecture II: Neutrino sources
Neutrinos number from an experiment
Flux from extraterrestrial sources, Sun in the first place
The lack of Sun neutrinos
Atmospheric neutrinos
The oscillating neutrino conjecture

Lecture III: Neutrino state oscillations
Description of neutrino oscillations, necessary conditions
Experiments, the present states
The planned experiments