Y In 1905 Lebesgue tried to prove the ( correct ) result that a function implicitly defined by a Baire function is Baire .
Lebesgue 's proof incorrectly assumed that the projection of a Borel set is Borel .
Y In 1905 Lebesgue tried to prove the ( correct ) result that a function implicitly defined by a Baire function is Baire , but his proof incorrectly assumed that the projection of a Borel set is Borel .