Section If.
Variables (pred_f then_f else_f : formula R).
Definition If := (pred_f /\ then_f \/ ~ pred_f /\ else_f)%T.

Lemma eval_Pick e (qev := qf_eval e) :
let P i := qev (pred_f i) in
qev Pick = (if pick P is Some i then qev (then_f i) else qev else_f).