Major Section: PROGRAMMING
An ACL2 ordinal is either a natural number or, for an infinite ordinal, a
list whose elements are exponent-coefficient pairs (see o-p). In the latter
case, this function returns the car of the first pair in the list. In
the case of a natural number, the value returned is 0 (since a natural
number, n, can be thought of as (w^0)n).
For the corresponding coefficient, see o-first-coeff.