Proof (truth) in the context of "Necessity and sufficiency"

Pramana (Sanskrit: प्रमाण; IAST: Pramāṇa) literally means "proof" and "means of knowledge". One of the core concepts in Indian epistemology, pramanas are one or more reliable and valid means by which human beings gain accurate, true knowledge. The focus of pramana is how correct knowledge can be acquired, how one knows, how one does not know, and to what extent knowledge pertinent about someone or something can be acquired.

While the number of pramanas varies widely from system to system, many ancient and medieval Indian texts identify six pramanas as correct means of accurate knowledge and attaining to the truth. Three of these are almost universally accepted: perception (pratyakṣa), inference (anumāna), and "word" (śabda), meaning the testimony of past or present reliable experts. The other three pramanas are more contentious: comparison and analogy (upamāna); postulation or derivation from circumstances (arthāpatti); and non-perception, or proof from absence (anupalabdhi). Each of these are further categorized in terms of conditionality, completeness, confidence, and possibility of error.

Demonstration involves showing by reason or proof, explaining or making clear by use of examples or experiments. Put more simply, demonstration means 'to clearly show'.

Proof of work (also written as proof-of-work, an abbreviated PoW) is a form of cryptographic proof in which one party (the prover) proves to others (the verifiers) that a certain amount of a specific computational effort has been expended. Verifiers can subsequently confirm this expenditure with minimal effort on their part. The concept was first proposed by Moni Naor and Cynthia Dwork in 1993 as a way to deter denial-of-service attacks and other service abuses such as spam on a network by requiring some work from a service requester, usually meaning processing time by a computer. Extending the work of Cynthia Dwork and Moni Naor, Adam Back formally described a proof of work system called Hashcash as a protection against email spam in 1997. The term "proof of work" was first coined and formalized in a 1999 paper by Markus Jakobsson and Ari Juels. The concept was adapted to digital tokens by Hal Finney in 2004 through the idea of "reusable proof of work" using the 160-bit secure hash algorithm 1 (SHA-1).

Proof of work was later popularized by Bitcoin as a foundation for consensus in a permissionless decentralized network, in which miners compete to append blocks and mine new currency, each miner experiencing a success probability proportional to the computational effort expended. PoW and PoS (proof of stake) remain the two best known Sybil deterrence mechanisms. In the context of cryptocurrencies they are the most common mechanisms.