export type Invariant = void;
export type EvolutionInvariantPred<A> = (previous: A, current: A) => boolean;
export declare function evolutionInvariant<A>(description: string, pred: EvolutionInvariantPred<A>): Invariant;
export declare function implies(x: boolean, y: boolean): boolean;
/**
 * Implies, but treats 'undefined' as 'false'
 */
export declare function impliesU(x: boolean | undefined, y: boolean | undefined): boolean;