Basic logic algebras
A basic logic algebra or BL-algebra is a structure A = (A,∨,0,∧,1,·,→) such
that
(A,∨,0,∧,1) is a
bounded lattice,
(A,·,1) is a commutative monoid,
→ gives the residual of ·: x·y ≤ z ⇔ y ≤ x→z,
linearity: ( x→y) ∨( y→x) = 1, and
BL: x·(x→y) = x∧y.
Remark: The BL identity implies that the lattice is distributive.
A basic logic algebra is a FLe-algebra A = (A,∨,0,∧,1,·,→) such that
linearity: ( x→y) ∨( y→x) = 1, and
BL: x·(x→y) = x∧y.
Remark: The BL identity implies that the identity element 1 is the top of the lattice.
Let A and B be basic logic algebras. A morphism from A to B is a function h : A→B that is a homomorphism: h(x∨y) = h(x)∨h(y) and h(1) = 1 and h(x∧y) = h(x)∧h(y) and h(0) = 0 and h(x·y) = h(x)·h(y) and h(x→y) = h(x)→h(y) hold.