What is the symbol for the universal set?

What is the symbol for the empty set?

The universal set in enclosed inside the.....

What does A∩B mean?

Where A∩B is located on a Venn diagram:

What does A∪B mean?

Where A∪B is located on a Venn diagram:

What does A' mean?

What A' looks like on a Venn diagram:

(Green = lilac from prev. examples)

How would you explain conditional probability?

What is the notation for this?