• Definition − The set ∑+ is the infinite set of all possible strings of all possible lengths over ∑ excluding λ.

• Representation − ∑+ = ∑1 ∪ ∑2 ∪ ∑3 ∪……. ∑+ = ∑* − { λ }

• Example − If ∑ = { a, b } , ∑+ = { a, b, aa, ab, ba, bb,………..}