Let Pk(f) denote the density of and/or trees defining a boolean function f within the set of and/or trees with fixed number of variables k. We prove that there exists constant Bf such that Pk(f) ∼Bf ·k-L(f)-1 when k&ra;∞, where L(f) denote the complexity of f (i.e. the size of a minimal and/or tree defining f). This theorem has been conjectured by Danièle Gardy and Alan Woods together with its counterpart for distribution π defined by some critical Galton-Watson process. Methods presented in this paper can be also applied to prove the analogous property for π.