  In this article we discuss some numerical parts of the mirror conjecture. For
any 3 - dimensional Calabi - Yau manifold author introduces a generalization of
the Casson invariant known in 3 - dimensional geometry, which is called Casson
- Donaldson invariant. In the framework of the mirror relationship it
corresponds to the number of SpLag cycles which are Bohr - Sommerfeld with
respect to the given polarization. To compute the Casson - Donaldson invariant
the author uses well known in classical algebraic geometry degeneration
principle. By it, when the given Calabi - Yau manifold is deformed to a pair of
quasi Fano manifolds glued upon some K3 - surface, one can compute the
invariant in terms of "flag geometry" of the pairs (quasi Fano, K3 - surface).
