A proof which indirectly shows a mathematical object exists without providing a specific example or algorithm for producing an example. Nonconstructive proofs are also called existence proofs.
Nonconstructive Proof
See also
Constructive Proof, Existence Problem, Existence Theorem, ProofExplore with Wolfram|Alpha
References
Courant, R. and Robbins, H. "The Indirect Method of Proof." §2.4.4 in What Is Mathematics?: An Elementary Approach to Ideas and Methods, 2nd ed. Oxford, England: Oxford University Press, pp. 86-87, 1996.Hoffman, P. The Man Who Loved Only Numbers: The Story of Paul Erdős and the Search for Mathematical Truth. New York: Hyperion, p. 229, 1998.Referenced on Wolfram|Alpha
Nonconstructive ProofCite this as:
Weisstein, Eric W. "Nonconstructive Proof." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/NonconstructiveProof.html