What does this symbol $∈_$ mean? I know what $x ∈ A$ stand for but what difference there is if we write $x ∈_R A$ ?
For those who wonder where did I encounter this symbol it was on one of a lecture slides on cryptography, pseudo random generators section. The excerpt said the following :
For many cryptographic protocols, we need randomly chosen numbers $ ∈_ ℤ_ = [0,−1]$.
In cryptography literature usually $$x \in_{R} A,$$ stands for randomly and uniformly chosen from $A.$ If another distribution is implied $$x \in_{{\cal D}} A,$$ is used where $\cal D$ is a probability distribution on the set $A.$
Other authors prefer $$S \xleftarrow{R} x$$ or $$S \xleftarrow{\cal D} x$$ especially when writing pseudocode for an algorithm.