File: LENGTH_CONV.doc

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\DOC LENGTH_CONV

\TYPE {LENGTH_CONV : conv}

\SYNOPSIS
Computes by inference the length of an object-language list.

\KEYWORDS
conversion, list.

\DESCRIBE
For any object language list of the form {"[x1;x2;...;xn]"}, where {x1},
{x2}, ..., {xn} are arbitrary terms of the same type, the result of evaluating
{
   LENGTH_CONV "LENGTH [x1;x2;...;xn]"
}
\noindent is the theorem
{
   |- LENGTH [x1;x2;...;xn] = n
}
\noindent where {n} is the numeral constant that denotes the length of the
list.

\FAILURE
{LENGTH_CONV tm} fails if {tm} is not of the form {"LENGTH [x1;x2;...;xn]"} or
{"LENGTH []"}.

\ENDDOC