Read “having an index” as “having some specific index”, e.g. 42.
The probabilities add up because typed 1,2,3,4 are each probability 1⁄4 in total.
Read “having an index” as “having some specific index”, e.g. 42.
The probabilities add up because typed 1,2,3,4 are each probability 1⁄4 in total.