The Lattice of L-ideals of a ring is modular IWM April, 2015 Iffat Jahan Ramjas College, University of Delhi

Fuzzy sets were introduced by Zadeh with a view to apply it in approximate reasoning. If the closed unit interval [0,1] is replaced by a lattice L having least and greatest elements Then is called an L-subset in X. A fuzzy set in X is a mapping

The concept of L-fuzzy subset which is now known as L-subset is introduced by Goguen in the year 1967.

Rosenfeld applied fuzzy set theory in algebra by introducing the notions of fuzzy subgroupoids and fuzzy subgroups in Wang Jin Liu initiated the studies of lattice valued ring theory by introducing the definitions of fuzzy L-subrings and fuzzy L- ideals in 1983.

We denote by R a commutative ring and by a complete Heyting Algebra where ‘ ’ denotes the partial ordering of L, the join (sup ) and meet (inf ) of the elements of are denoted by ‘ ’ and ‘ ’ respectively.

L-subset An L-subset in a set X is a function The set of L-subsets of X is called the L-power set of X and is denoted by

For, We say that is contained in if for every and is denoted by..

For a family of L-subsets of X, where I is a nonempty index set, the union and the intersection of are respectively defined by : and for each.

Let. Define as follows: is called sum of and. By the definition of sum it follows that.

L -subring of R Let Then is said to be an L-subring of R if for each (i) (ii)

If is an L-subring of R, then and Moreover, and is known as the tip of

L-Ideal of a ring R Let be an L-subring of R. Then is said to be an L-( left, right ) ideal of R if for each ( ) The set of L-ideals of R is denoted by

The intersection of any arbitrary family of L-ideals of R is an L-ideal of R.

Let. Then the L-ideal generated by is defined to be the least L-ideal of R which contains. It is denoted by. That is

The set of L-ideals of a ring is a complete lattice under the ordering of L-set inclusion, where the infima and the suprema of a family of L-ideals of are defined as the intersection of the family and the ideal generated by their union respectively.

In ring theory, the sum of two ideals I and J of a ring R is again an ideal of R which is the least ideal of R containing both I and J. Thus The sum I+J provides the join of the ideals I and J.

However in L-ring theory, the sum of two L- ideals of R is an L-ideal containing both if and only if they have identical tips.

Let denote the set of L-ideals of R, each having the same tip ‘t’ by Thus is a modular lattice with meet and join defined by and.

However, if two L-ideals of R have different tips, then their sum fails to provide the join of given L-ideals.

Modularity of the lattice of L-ideals of a ring still remain an open problem.

T. Head in his outstanding paper introduced the concept of a tip-extended pair of fuzzy subgroups and provided the join structure of a pair of fuzzy subgroups of the lattice of fuzzy normal subgroups.

A. Jain demonstrated the utility of this join structure to establish a direct proof of modularity of the lattice of fuzzy normal subgroups.

We answer the question of modularity of the lattice of L-ideals of a ring in affirmative. In doing so, we extend the notion of tip-extended pair of fuzzy ideals to the L-setting for L-ideals of a ring and thus construct the join of two L- ideals in a very simple way. This join structure helps us to establish that the lattice of L-ideals of a ring is modular.

Here we introduce the idea of a tip-extended pair of L-ideals. We first prove the following proposition:

Let be an L-ideal of R and. Then the L- subset of R defined by if x  0, t if x = 0; is also an L-ideal of R.of

Let and be L-ideals of R. Define L-subsets and of R as follows: and for x  0,

It follows thatfollows are L-ideals of R

For L-ideals and of R, from the above proposition it follows that and are also L-ideals of R. We call the pair, the tip- extended pair of L-ideals. We also notice that

If and are L-ideals of R, then is the least L-ideal of R containing That is

The set of L-ideals of a ring is a lattice under the ordering of L-set inclusion, where the join ‘ ’ and the meet ‘ ’ in are defined as follows: and

The lattice of L-ideals of a ring R is modular.

Since modular inequality holds in every lattice, it is sufficient to establish that if and and then That is

I. Jahan, The lattice of L-ideals of a ring is modular, Fuzzy Sets and Systems 199 ( 2012) 121 – 129.I. Jahan, The lattice of L-ideals of a ring is modular, Fuzzy Sets and Systems 199 ( 2012) 121 – 129.

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A. Jain, Tom Head’s join structure of fuzzy subgroups, Fuzzy Sets and Systems 125 (2002) 191 – 200. I. Jahan, The lattice of L-ideals of a ring is modular, Fuzzy Sets and Systems 199 ( 2012) 121 – 129. W. – J. Liu, Operations on fuzzy ideals, Fuzzy Sets and Systems 11 (1983) 31 – 41.

J. N. Mordeson and D. S. Malik, Fuzzy commutative algebra, World Scientific Pub. Co. Pte. Ltd., A. Rosenfeld, Fuzzy groups, J. Math. Anal. Appl. 35 (1971) 512 – 517. L. A. Zadeh, Fuzzy Sets, Information and Control 8 (1965) 338 – 353.