Conversion to perform exponentiation on a rational literal of type :real.
The call REAL_RAT_POW_CONV `c pow n` where c is a rational literal of
type :real and n is a numeral of type :num, returns |- c pow n = d
where d is the canonical rational literal that is equal to c raised to the
nth power. The literal c may be an integer literal (&n or -- &n),
a ratios (&p / &q or -- &p / &q), or a decimal (#DDD.DDDD or
#DDD.DDDDeNN). The result d is always put in the form &p / &q or
-- &p / &q with q > 1 and p and q sharing no common factor, or simply
&p or -- &p when that is impossible.
Fails if applied to a term that is not a permitted rational literal of type
:real raised to a numeral power.
# REAL_RAT_POW_CONV `#1.414 pow 2`;;
val it : thm = |- #1.414 pow 2 = &1999396 / &1000000