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denotes a data structure which represents the term
. We shall refer to the brackets around
as Gödel brackets, and to
as the quoted version of
. We shall refer to the value of a quote as a parse tree.
has many, unusual properties. Among others, it does not respect substitution of equals. As an example, the value of
differs from the value of
even though
. If one asks Logiweb to compute the value of
, the value will be
.
Maybe even more surprising, if one asks Logiweb to compute
, then that value will also be
. That is so because
does not just denote the term
as such. Each instance of
denotes that particular instance of
. Each instance contains so-called debugging information which encodes the exact location of the instance on the page. Among others, that debugging information is used when generating meaningful error messages.
One may think of debugging information as a sort of 'radioactive mark' on a term. The mark does not really affect the properties of the term, but it allows to trace a term through processes like macro and tactic expansion.
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