?A ____ is a data network connection that makes use of the public telecommunications infrastructure but maintains privacy through the use of a tunneling protocol and security procedures.

Stream reduction operation ________ uses the elements of a collection to produce a single value using an associative accumulation function (e.g., a lambda that adds two elements).

a. reduce b. condense c. combine d. associate

Denotational semantics are based on the formal mathematical model called the ______.

Fill in the blank(s) with the appropriate word(s).