illustrate the statement projection operation

Question

Illustrate the statement 'Projection operation distributes over the union operation'. Give an example.   

Ans: Π_L(E₁ ∪ E₂) = (Π_L(E₁)) ∪ (Π_L(E₂))  

This says that result acquired by projecting on an attribute set A, after taking union of two relations is similar as union of two relations each of which is a projection of original relations on A.