Conversion to produce signum (sign) of a rational literal of type :real.
DESCRIPTION
The call REAL_RAT_SGN_CONV `real_sgn c`, where c is a rational literal of
type :real, returns the theorem |- real_sgn c = d where d is the
canonical rational literal that is equal to c's sign. The literal c may be
an integer literal (&n or -- &n), a ratio (&p / &q or -- &p / &q), or a
decimal (#DDD.DDDD or #DDD.DDDDeNN). The returned value d is always put
in the form &1, &0 or -- &1.
FAILURE CONDITIONS
Fails if applied to a term that is not the signum function applied to
one of the permitted forms of rational literal of type :real.
EXAMPLE
# REAL_RAT_SGN_CONV `real_sgn(-- &3 / &2)`;;
val it : thm = |- real_sgn (-- &3 / &2) = -- &1