In mathematics, an algebraic structure
Contents
- Definition
- Addition
- Multiplication
- Linear PTR
- Connection with projective planes
- Related algebraic structures
- References
There is wide variation in the terminology. Planar ternary rings or ternary fields as defined here have been called by other names in the literature, and the term "planar ternary ring" can mean a variant of the system defined here. The term "ternary ring" often means a planar ternary ring, but it can also simply mean a ternary system.
Definition
A planar ternary ring is a structure
-
T ( a , 0 , b ) = T ( 0 , a , b ) = b , ∀ a , b ∈ R ; -
T ( 1 , a , 0 ) = T ( a , 1 , 0 ) = a , ∀ a ∈ R ; -
∀ a , b , c , d ∈ R , a ≠ c , there is a uniquex ∈ R such that :T ( x , a , b ) = T ( x , c , d ) ; -
∀ a , b , c ∈ R , there is a uniquex ∈ R , such thatT ( a , b , x ) = c ; and -
∀ a , b , c , d ∈ R , a ≠ c , the equationsT ( a , x , y ) = b , T ( c , x , y ) = d have a unique solution ( x , y ) ∈ R 2
When
No other pair (0', 1') in
Addition
Define
Multiplication
Define
Linear PTR
A planar ternary ring
Connection with projective planes
Given a planar ternary ring
Let
Then define,
Every projective plane can be constructed in this way, starting with an appropriate planar ternary ring. However, two nonisomorphic planar ternary rings can lead to the construction of isomorphic projective planes.
Conversely, given any projective plane π, by choosing four points, labelled o, e, u, and v, no three of which lie on the same line, coordinates can be introduced in π so that these special points are given the coordinates: o = (0,0), e = (1,1), v = (
Linearity of the PTR is equivalent to a geometric condition holding in the associated projective plane.
Related algebraic structures
PTR's which satisfy additional algebraic conditions are given other names. These names are not uniformly applied in the literature. The following listing of names and properties is taken from Dembowski (1968, p. 129).
A linear PTR whose additive loop is associative (and thus a group ), is called a cartesian group. In a cartesian group, the mappings
must be permutations whenever
A quasifield is a cartesian group satisfying the right distributive law:
A semifield is a quasifield which also satisfies the left distributive law:
A planar nearfield is a quasifield whose multiplicative loop is associative (and hence a group). Not all nearfields are planar nearfields.