Fractions of integers (with b nonzero) are known as rational numbers. The set of all such irreducible fractions is commonly denoted ⁠ Q ⁠. There is still a minor obstacle for ⁠ ( Q , ⋅ ⋅ ) ⁠, the rationals with multiplication, being a group: because zero does not have a multiplicative inverse (i.e., there is no x such that ⁠ x ⋅ ⋅ 0 = 1 ⁠), ( Q , ⋅ ⋅ ) is still not a group.