Input Output HK, a development studio behind the Cardano (ADA) blockchain, has released a technical explanation of Hardfork Combinator operations in the process of the Shelley mainnet deployment.
Hardfork Combinator that allows avoiding hardfork
According to the official announcement by IOHK on the Cardano (ADA) forum, the concept of the Hardfork Combinator is designed to avoid a chain split in its common understanding. It allows a seamless transition from the Byron semi-decentralized phase to Shelley mainnet.

The new instrument is being deployed to the testnet environment. The Cardano Foundation has released a video with a detailed technical explanation of how it works. Philipp Kant, Director of Formal Methods in IOHK, showcased the codebase and demonstrated why it was created this way.
This Combinator allows a smooth transition from Byron to Shelley for every node of the Cardano (ADA) blockchain. Without this instrument, a disagreement could evolve between different nodes.
Once that occurs, different versions of the protocol can start existing which, in turn, may lead to severe conflict between different parts of the blockchain.
One node, two protocols
With this combinator, one node can operate under various protocols at the same time. According to Mr. Tim Harrison, marketing and communications director of Input Output HK, the Combinator is crucial for the switch between the two stages of Cardano (ADA) progress:
While running the first protocol (i.e. Byron), it can be triggered by a special on-chain update whereupon it manages the smooth transition to running the next protocol (i.e. Shelley).
The codebase of the Hardfork Combinator has been successfully tested and is ready for deployment in the mainnet.
Mr. Kant explains the top distinct features of the new release and their role in the very sensitive transition process in a video posted on the official Cardano (ADA) forum.
As covered by U.Today Crypto News, Cardano (ADA) is going to launch the Shelley mainnet in a few weeks. Currently, the process of development is going through the public testing stage after a successful ITN testnet and friends&family testnet.