| |
| | AlgebraicStructures - PineWiki |
 | | Let A be the free monoid over { a, b, c }, and let B be the subalgebra generated by aaa. |
 | | In a free semigroup, x(yz) = (xy)z, always, because of the associativity axiom, but xy is never equal to x for any x and y, xy is never equal to yx, etc. In a free monoid, xe = ex = x, but xy is never equal to x unless y = e, and so forth. |
 | | Fortunately this reversal operation is an isomorphism between the two monoids, and in general we can show that any free algebra for a given class with a given base set is unique up to isomorphism, which means that while there may be more than one such algebra, there is only one isomorphism equivalence class. |
| pine.cs.yale.edu /pinewiki/AlgebraicStructures (5539 words) |
|