**Joseph Louis Lagrange**(1736-1813)- Born in France.
- He applied mathematical analysis toprinciples estalished by Sir Isaac Newton to problems of astronomy.
- He presided over the commission that introduced the metric system in 1793.

**Antoine de Laloubère**(1600-1664)- Born in France.
- He was the first mathematician to study the properties of the helix.

**Pierre Simon Laplace**(1749-1827)- Born in France.
- He developed the theory of probability.

**Henri Léon Lebesgue**(1875-1941)- Born in France.
- He developed a new theory, known as the Lesbesgue integral theory.
- He made contributions to set theory, the calculus of variations, and function theory.

**Adrien-Marie Legendre**(1752-1833)- Born in France.
- He established the law of reciprocity of quadric residues and the law of the distribution of prime numbers.
- He provided proof of the irrationability of
*pi*and*pi-squared*. - He published a textbook and tables on elliptical functions.

**Gottfried Wilhelm Leibniz**(1646-1716)- Born in Germany.
- He determined that the sum of the reciprocals of the triangular numbers equals 2.
- He discovered the fundamental principles of calculus.

**Marius Sophus Lie**(1842-1899)- Born in Norway.
- He discovered the transformation by which a sphere can be made to correspond to a straight line.
- He also discovered that theoroms on aggregates of lines can be translated into theoroms on aggregates of spheres.
- He developed the general theory of finite continuous groups of substitutions.

**Nikolai Ivanovich Lobachevsky**(1792-1856)- Born in Russia.
- He founded non-Euclidean geometry concurrently with, but independently of, Karl Gauss and János Bolyai.
- He showed that two geometric figures cannot have the same shape but different sizes.