"Abstraction of [[numeric types|Numeric]] that may be raised 
 to a power using the _exponentiation_ operator ^.
     function exp(Float x) => e^x;
 The exponentiation operation should obey the usual index
 laws, including:
 - `x^0 = 1`,
 - `x^1 = x`,
 - `x^(-1) = 1/x` 
 - `x^(m+n) = x^m * x^n`
 - `x^(m-n) = x^m / x^n`
 - `x^(m*n) = (x^m)^n`
 - `(x*y)^n = x^n * y^n`
 where `0` is the additive identity, and `1` is the 
 multiplicative identity.
 Note that in general, the type of the exponent may be 
 different to the numeric type which is exponentiated. For
 example, a `Rational` number class might be a subtype of
 `Exponentiable<Rational,Integer>`, thus accepting only
 whole-number exponents."
see (`class Integer`, `class Float`)
shared interface Exponentiable<This,Other> of This
        satisfies Numeric<This>
        given This satisfies Exponentiable<This,Other> 
        given Other satisfies Numeric<Other> {

    "The result of raising this number to the given power."
    shared formal This power(Other other);