Question: When was the sugar-free soft drink which was a later entrant to the diet cola market unveiled 
Sentence (from "Diet Pepsi"): Diet Pepsi and Diet Pepsi Classic Formula Blend (stylized as diet PEPSI CLASSIC SWEETENER BLEND) are no-calorie carbonated cola soft drinks produced by PepsiCo, introduced in 1964 as a variant of Pepsi-Cola with no sugar.
Relevant evidence: No