- Moved abs_def to drule.ML
- elim_defs now takes a boolean argument which controls the automatic
expansion of theorems mentioning constants whose definitions are
eliminated
consts fib :: nat => nat
recdef fib "measure(%n. n)"
"fib 0 = 0"
"fib 1 = 1"
"fib (Suc(Suc x)) = fib x + fib (Suc x)"