What does Delta mean in this case

[rad0786]

Homework Statement

R = { (X,Y) $$\epsilon$$ P(A) x P(A) / (X$$\Delta$$Y) $$\subseteq$$ B}

(X$$\Delta$$Y) $$\subseteq$$ B - what does delta mean?

Homework Equations

The Attempt at a Solution

 

[HallsofIvy]

Probably "symmetric difference": A union B \ A intersect B: that is, all points that are in A or B but [/b]not[/b] in both.

 

[Architeuthis Dux]

In this context, delta refers to the symmetric difference between two sets, denoted by the symbol \Delta. The symmetric difference of two sets, X and Y, is the set of elements that are in either X or Y, but not both. In other words, it is the set of elements that are in either X or Y, but not in their intersection. The notation (X\DeltaY) \subseteq B indicates that the symmetric difference of X and Y is a subset of the set B. This means that all elements in the symmetric difference of X and Y are also elements of B.