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What is the "closure" of a function?

Subject: What is the "closure" of a function?
From: "Dimitre Novatchev dnovatchev@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>
Date: Fri, 23 May 2014 20:28:19 -0000
 What is the "closure" of a function?
 The Functions and Operators 3.0 recommendation
(http://www.w3.org/TR/xpath-functions-30/) uses the term "closure" of
a function:

"In effect, the static and dynamic part of the context thus act as
part of the closure of the function item."

However, there is no formal definition of "closure".

A search for "closure " in the Data-Model 3.0" Recommendation yields 0 results.

However, the XDM defines the so called "nonlocal variable bindings":

"nonlocal variable bindings (a mapping from xs:QName to item()*): This
provides a value for each of the function's free variables (i.e.,
variables referenced by the function's implementation, other than
locals and parameters)."

My question is:

  Is it safe to assume that what is referred to as the "closure"
property of functions in the F & O document is the same as the
"nonlocal variable bindings" property of functions, defined in the

Dimitre Novatchev
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