constructive >> /kənˈstrəktɪv/
Definition: [adjective] Serving a useful purpose; tending to build up.
Example: constructive criticism
Definition: [adjective] Derived by inference; implied by operation of law; not obvious or explicit.
Example: constructive liability
Definition: [adjective] Relating to, based on, or denoting mathematical proofs which show how an entity may in principle be constructed or arrived at in a finite number of steps.
Example: He made a good start to solving this problem for n = 2 when he found a constructive proof of a finite basis for binary forms.