Lhss-length
Get the length of the lhsarr array.
In the execution this just gets the array length. The
logical definition is just a wrapper for len:
Function: lhss$a-length
(defun lhss$a-length (lhsarr$a)
(declare (xargs :guard (lhsarr$ap lhsarr$a)))
(len lhsarr$a))
