Three-local Conserved Charge Implies Quantum Integrability

It is shown that the conservation of a local charge supported by three neighboring sites, or its local version, Reshetikhin's condition, suffices to guarantee the existence of all higher conserved charges and hence the integrability of a quantum spin chain. This establishes Grabowski and Mathieu's long-standing conjecture as a theorem, ending the folklore that the existence of higher conserved charges imposes additional constraints not implied by the conservation of the three-local charge.