**Statement:** Observation induces transition from superposition to definite eigenstate.
Definition: P is a projection iff P² = P = P†.
Eigenvalue structure: Projections have eigenvalues 0 and 1 only.
Collapse as projection: |ψ⟩ → P_a|ψ⟩/||P_a|ψ⟩|| where P_a = |a⟩⟨a|.