What this symbols means regarding groups

[transgalactic]

i got two groups of numbers "a" and "b"

what is the meaning of a\b and b\a

??

 

[HallsofIvy]

Do you mean "groups" in the algebraic sense or just sets of numbers. Typically, if a and b are sets "a\b" means all members of a that are NOT in b. It is the same a intersect (complement b).

When you are dealing specifically with sets of numbers you should be careful to distinguish that from "a- b" which means the set of all numbers that can be formed by subtracting a number in b from a number in a.