| Answer | Crossword Clue |
|---|---|
| groupoid | algebraic system closed under a binary operation |
| semigroup | a mathematical group that is closed under an associative binary operation |
| semigroups | SEMIGROUP, a mathematical group that is closed under an associative binary operation |
| ring | set of mathematical elements that is closed under two binary operations of which the first forms a commutative group with the set and the second is associative over the set and is distributive with respect to the first operation |
