A function f(x) is said to be continuous at x=a from the left if the limit of f(x) as x->a- is f(a), and continuous at x=a from the right if the limit of f(x) as x->a+ is f(a). In particular, a function is continuous at x=a if and only if it is continuous from both the left and the right. On the other hand, a function is sometimes said to have a one-sided continuity at x=a if it is continuous from either the left or the right, but not both.