One-sided limit
In calculus, a one-sided limit refers to either one of the two limits of a function f ( x ) {\displaystyle f(x)} of a real variable x {\displaystyle x} as x {\displaystyle x} approaches a specified point either from the left or from the right. The limit, as x {\displaystyle x} decreases in value approaching a {\displaystyle a} ( x {\displaystyle x} approaches a {\displaystyle a} "from the right" or "from above"), is denoted: lim x → a + f ( x ) or lim x ↓ a f ( x ) or lim x ↘ a f ( x ) or f ( a + ) .