This formal note is the first in a series of formal supplements to Version 9.0 of the c²-Model of Realities. It develops the minimal selection condition of observable reality: S_obs = S_stable ∩ S_accessible The note focuses on stability and accessibility as elementary conditions of observability. It introduces stability and accessibility indicators, discusses appearance time, and presents a minimal toy model: V_1(x) = Σ(x) A(x) The note does not introduce a new version of the c²-model and does not claim empirical confirmation. Current examples from precision pion physics, long-lived particle searches, quantum measurement contexts, collapse-model discussions, early JWST cosmology, and consciousness-related discussions are used only as structural motivation. This work is intended as a formal supplement to Version 9.0 and as a first step toward further mathematical and simulation-oriented elaboration of the c²-framework.