Suppose A is the set of students in your class who were absent on Tuesday and B the set of students who were absent on Wednesday. Then,
A = {Roja, Ramu, Ravi} and
B = {Ramu, Preethi, Haneef}
Now, we want to find K, the set of students who were absent on either Tuesday or Wednesday. Then, does Roja `in` Κ? Ramu `in` Κ? Ravi `in` Κ? Haneef `in` Κ? Preeti `in` Κ? Akhila `in` Κ?

Answer

`A uu B = {x : x in A or x in B}`