FIRSTN_CONV
listLib.FIRSTN_CONV : conv
Computes by inference the result of taking the initial n elements of a list.
For any object language list of the form “[x0;...x(n-k);...;x(n-1)]” ,
the result of evaluating
FIRSTN_CONV “FIRSTN k [x0;...x(n-k);...;x(n-1)]”
is the theorem
|- FIRSTN k [x0;...;x(n-k);...;x(n-1)] = [x0;...;x(n-k)]
Failure
FIRSTN_CONV tm fails if tm is not of the form described above, or
k is greater than the length of the list.