Dedekind cut
(i) ∅ ≠ A ≠ ℚ.
(ii) if x < y are rational numbers and y ∈ A, then x ∈ A.
(iii) if x ∈ A, then there exists y ∈ A such that x < y.
A Dedekind cut A then represents the real number that is its supremum but without having to make reference to real numbers. Order can be defined by A ≤ B if and only if A⊆B and addition by 
The other arithmetic operations can also be defined but are a little more involved as care must be taken with signs.
- latent root
- latent vector
- LaTeX
- Latin square
- latitude
- lattice
- lattice
- latus rectum
- Laurent expansion
- law
- law of averages
- laws of large numbers
- lcm
- leading coefficient
- leading diagonal
- least action, principle of
- least common denominator
- least common multiple
- least squares
- least squares theorem
- least upper bound
- least value
- leaving variable
- Lebesgue, Henri
- Lebesgue integration