This was used by Riemann in 1851 .
Weierstrass found a counterexample to one version of this principle in 1870 , and Hilbert stated and proved a correct version in 1900 .
This was used by Riemann in 1851 , but Weierstrass found a counterexample to one version of this principle in 1870 , and Hilbert stated and proved a correct version in 1900 .