SYMMETRICAL HEYTING ALGEBRAS WITH OPERATORS by LUISA ITURRIOZ in Villeurbanne (France) S,x v i S , x = 1 , with i x = 5 3 0 .
3*
LUISA ITUIhRIOZIt follows from the above definition and from the fact that the class of all symmetrical Heyting algebras is equationally definable ([30], [34]) that the class of all symmetrical Heyting algebras of order n is also equationally definable. We will refer to a SHalgebra A of order n, for short.A SH-algebra A of order n is said to be non-degenerate if it is a non-degenerate algebra, i.e. if it contains a t least two different elements. If (A, 0, 1, A, v, a , 1, -, S,) is a SH-algebra of order 2, then S,x = z for all 5 E A and (A, 0 , 1, A, v, a, i , -) is a symmetrical Boolean algebra ([20]), noted SB-algebra for short. We are going t o see later that SH-algebras of order 3 are equivalent to involutive three-valued Heyting algebras studied in [14] and [15].
3.2.