rator
Term.rator : term -> term
Returns the operator from a combination (function application).
If M is a combination, i.e., has the form (t1 t2), then rator M returns t1.
M
(t1 t2)
rator M
t1
Fails if M is not a combination.
Term.rand, Term.dest_comb
Term.rand
Term.dest_comb