This repository contains a TypeScript library for deep merging JavaScript/TypeScript objects while preserving and inferring accurate type information in the merged result. The library provides both immutable (`deepmerge`) and mutable (`deepmergeInto`) variants, along with customizable versions (`deepmergeCustom`, `deepmergeIntoCustom`) that allow developers to tailor the merging behavior for specific data types or scenarios. The architecture features a clean separation of concerns: core merging logic, utility functions for object inspection and type-level operations, default merging strategies for different data types (objects, arrays, sets, maps), and sophisticated type definitions that track how types evolve through the merging process. The implementation handles edge cases correctly, including prototype pollution protection, non-enumerable properties, and symbols. Notably, the library has zero runtime dependencies, demonstrating a commitment to self-contained, reliable code. The type system is particularly impressive, using advanced TypeScript features to ensure that the merged result's type accurately reflects the combination of input types.