Identifying an Unknown Symbol in a Passage

[Miike012]

Homework Statement

I am reading this passage and I came across a symbol that I am unfamiliar with... it is the highlighted portion of the paragraph.

Homework Equations

The Attempt at a Solution

 

[TylerH]

http://en.wikipedia.org/wiki/Set_(mathematics)#Intersections

It returns a set containing the members that are in both sets. The passage is saying that f + g is only defined where BOTH f AND g are defined.

 

[ebits21]

It's the symbol for an intersection in set theory. So, it refers to the elements that are common to both sets.

For example, if you had these two sets:
{1,2,3,4}
{3,4,5,6}

The elements common to both sets would be 3 and 4. (Where the two sets intersect).

 

[Miike012]

Thank you, that makes sence.