/**
 * Subtyping checker for Dvala's set-theoretic type system.
 *
 * Subtyping is semantic: S <: T iff the set of values denoted by S
 * is a subset of the set denoted by T.
 *
 * Key rules:
 * - Never <: T for all T (empty set is subset of everything)
 * - T <: Unknown for all T (everything is subset of universal set)
 * - Primitive <: Primitive iff same name
 * - Literal <: Primitive iff the literal's type matches
 * - Function: contravariant params, covariant return
 * - Record: width subtyping (more fields <: fewer fields) + depth subtyping
 * - Union: S1|S2 <: T iff S1 <: T and S2 <: T
 * - Intersection: S <: T1&T2 iff S <: T1 and S <: T2
 * - Negation: S <: !T iff S & T = Never (S and T are disjoint)
 */
import type { Type } from './types';
/**
 * Check whether S is a subtype of T (S <: T).
 * Uses a visited set for cycle detection (recursive types).
 */
export declare function isSubtype(s: Type, t: Type): boolean;