Constructibility

In mathematics, there are several notions of constructibility:

• a point in the Euclidean plane that can be constructed with unruled straightedge and compass. Also, any complex number associated to such a point; see constructible number.
• a regular polygon that can be constructed with unruled straightedge and compass; see constructible polygon.
• a theorem that can be proved by constructivist logic; see mathematical constructivism.
• a set in Kurt Gödel's universe L, which may be constructed by transfinite application of certain constructions in set theory; see constructible universe.