modify eval:lambda to make supporting lexical scope easier
modify sqrt testcase to use lexical scope with 'define' syntax sugar
update Lisp special forms doc
modify define_stmt_sugar
factorial testcase
fibonacci testcase
count_change testcase
take quite a while to compute (count-change 100)
add is_integer()
add builtin_mod()
add exponential testcase
gcd and O(sqrt(n)) primality testcases
add builtin_random
add fermat primality test
add a Carmichael number (561) that fools Fermat test