Proof by construction, or proof by example, is the construction of a concrete example with a property to show that something having that property exists. Joseph Liouville, for instance, proved the existence of transcendental numbers by constructing an explicit example. It can also be used to construct a counterexample to disprove a proposition that all elements have a certain property.

Two-column proof
গঠন দ্বারা প্রমাণ
সম্ভাব্যতার দ্বারা প্রমাণ
প্রকৃতি ও উদ্দেশ্য