 In the 18th and 19th centuries, there was much work on irrational and transcendental numbers.Johann Heinrich Lambert (1761) gave the first flawed proof that cannot be rational; Adrien-Marie Legendre (1794) completed the proof, and showed that is not the square root of a rational number.Paolo Ruffini (1799) and Niels Henrik Abel (1842) both constructed proofs of the Abel–Ruffini theorem