LENGTH_CONV : conv
STRUCTURE
listLib
SYNOPSIS
Computes by inference the length of an object-language list.
DESCRIPTION
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]”
is the theorem 
   |- LENGTH [x1;x2;...;xn] = n
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 []”.
HOL  Kananaskis-13