Constructive proof

In mathematics, a constructive proof is a method of proof that shows the existence of a mathematical object—by giving a method on how to create the object. The other type of proof is called non-constructive proof, or existence proof: It shows that an object must exist, but does not give a way how to construct it.
A non-constructive proof is rejected by the so-called constructivists, who choose to interpret existence in a stricter way.