package alba

find p start beyond returns i with start <= i < beyond and p i or i = beyond if no index in the interval satisfies the predicate p.

exist p start beyond

Is there an index i satisfying p i within start <= i < beyond?

forall p start beyond

Do all indices i within start <= i < beyond satisfy p i?

fold a f start beyond starts with value a and folds the function f over the interval start..beyond.

fold a f start beyond =

   f (beyond - 1) (...  (f (start+1) (f start a)))