algebra.lattice
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Boolean algebras are Heyting algebras with the additional constraint that the law of the excluded middle is true (equivalently, double-negation is true).
Boolean algebras are Heyting algebras with the additional constraint that the law of the excluded middle is true (equivalently, double-negation is true).
This means that in addition to the laws Heyting algebras obey, boolean algebras also obey the following:
- (a ∨ ¬a) = 1
- ¬¬a = a
Boolean algebras generalize classical logic: one is equivalent to
"true" and zero is equivalent to "false". Boolean algebras provide
additional logical operators such as xor
, nand
, nor
, and
nxor
which are commonly used.
Every boolean algebras has a dual algebra, which involves reversing true/false as well as and/or.
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Every Boolean ring gives rise to a Boolean algebra:
Every Boolean ring gives rise to a Boolean algebra:
- 0 and 1 are preserved;
- ring multiplication (
times
) corresponds toand
; - ring addition (
plus
) corresponds toxor
; a or b
is then defined asa xor b xor (a and b)
;- complement (
¬a
) is defined asa xor 1
.
A bounded distributive lattice is a lattice that both bounded and distributive
A bounded distributive lattice is a lattice that both bounded and distributive
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A bounded lattice is a lattice that additionally has one element that is the bottom (zero, also written as ⊥), and one element that is the top (one, also written as ⊤).
A bounded lattice is a lattice that additionally has one element that is the bottom (zero, also written as ⊥), and one element that is the top (one, also written as ⊤).
This means that for any a in A:
join(zero, a) = a = meet(one, a)
Or written using traditional notation:
(0 ∨ a) = a = (1 ∧ a)
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De Morgan algebras are bounded lattices that are also equipped with a De Morgan involution.
De Morgan algebras are bounded lattices that are also equipped with a De Morgan involution.
De Morgan involution obeys the following laws:
- ¬¬a = a
- ¬(x∧y) = ¬x∨¬y
However, in De Morgan algebras this involution does not necessarily provide the law of the excluded middle. This means that there is no guarantee that (a ∨ ¬a) = 1. De Morgan algebra do not not necessarily provide the law of non contradiction either. This means that there is no guarantee that (a ∧ ¬a) = 0.
De Morgan algebras are useful to model fuzzy logic. For a model of classical logic, see the boolean algebra type class implemented as Bool.
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A distributive lattice a lattice where join and meet distribute:
A distributive lattice a lattice where join and meet distribute:
- a ∨ (b ∧ c) = (a ∨ b) ∧ (a ∨ c)
- a ∧ (b ∨ c) = (a ∧ b) ∨ (a ∧ c)
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Generalized Boolean algebra, that is, a Boolean algebra without the top element. Generalized Boolean algebras do not (in general) have (absolute) complements, but they have ''relative complements'' (see GenBool.without).
Generalized Boolean algebra, that is, a Boolean algebra without the top element. Generalized Boolean algebras do not (in general) have (absolute) complements, but they have ''relative complements'' (see GenBool.without).
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Every Boolean rng gives rise to a Boolean algebra without top:
Every Boolean rng gives rise to a Boolean algebra without top:
- 0 is preserved;
- ring multiplication (
times
) corresponds toand
; - ring addition (
plus
) corresponds toxor
; a or b
is then defined asa xor b xor (a and b)
;- relative complement
a\b
is defined asa xor (a and b)
.
BoolRng.asBool.asBoolRing
gives back the original BoolRng
.
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Heyting algebras are bounded lattices that are also equipped with
an additional binary operation imp
(for implication, also
written as →).
Heyting algebras are bounded lattices that are also equipped with
an additional binary operation imp
(for implication, also
written as →).
Implication obeys the following laws:
- a → a = 1
- a ∧ (a → b) = a ∧ b
- b ∧ (a → b) = b
- a → (b ∧ c) = (a → b) ∧ (a → c)
In heyting algebras, and
is equivalent to meet
and or
is
equivalent to join
; both methods are available.
Heyting algebra also define complement
operation (sometimes
written as ¬a). The complement of a
is equivalent to (a → 0)
,
and the following laws hold:
- a ∧ ¬a = 0
However, in Heyting algebras this operation is only a pseudo-complement, since Heyting algebras do not necessarily provide the law of the excluded middle. This means that there is no guarantee that (a ∨ ¬a) = 1.
Heyting algebras model intuitionistic logic. For a model of
classical logic, see the boolean algebra type class implemented as
Bool
.
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A join-semilattice (or upper semilattice) is a semilattice whose operation is called "join", and which can be thought of as a least upper bound.
A join-semilattice (or upper semilattice) is a semilattice whose operation is called "join", and which can be thought of as a least upper bound.
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A lattice is a set A
together with two operations (meet and
join). Both operations individually constitute semilattices (join-
and meet-semilattices respectively): each operation is commutative,
associative, and idempotent.
A lattice is a set A
together with two operations (meet and
join). Both operations individually constitute semilattices (join-
and meet-semilattices respectively): each operation is commutative,
associative, and idempotent.
Join can be thought of as finding a least upper bound (supremum), and meet can be thought of as finding a greatest lower bound (infimum).
The join and meet operations are also linked by absorption laws:
meet(a, join(a, b)) = join(a, meet(a, b)) = a
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Logic models a logic generally. It is a bounded distributive lattice with an extra negation operator.
A meet-semilattice (or lower semilattice) is a semilattice whose operation is called "meet", and which can be thought of as a greatest lower bound.
A meet-semilattice (or lower semilattice) is a semilattice whose operation is called "meet", and which can be thought of as a greatest lower bound.
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