AUTHORS:
Elements of free monoids are represented internally as lists of pairs of integers.
Bases: sage.structure.element.MonoidElement
Element of a free monoid.
EXAMPLES:
sage: a = FreeMonoid(5, 'a').gens()
sage: x = a[0]*a[1]*a[4]**3
sage: x**3
a0*a1*a4^3*a0*a1*a4^3*a0*a1*a4^3
sage: x**0
1
sage: x**(-1)
...
TypeError: bad operand type for unary ~: 'FreeMonoidElement'