Converts OCaml number to canonical rational literal of type :real.
DESCRIPTION
The call term_of_rat n, where n is an OCaml rational number (type num),
returns the canonical rational literal of type :real that represents it. The
canonical literals are integer literals &n for numeral n, -- &n for a
nonzero numeral n, or ratios &p / &q or -- &p / &q where p is nonzero,
q > 1 and p and q share no common factor.
FAILURE CONDITIONS
Never fails.
EXAMPLE
# term_of_rat (Int 3 // Int 2);;
val it : term = `&3 / &2`