eq = (a, b) => {
  let retval = null
  if (!(atom(a) && atom(b)))
    retval = undefined
  else
    retval = (a == b)
  debug && log_debug("eq?", a, b, ':', retval)
  return retval
}

assert(eq('A', 'A'))
assert(!eq(cons('A', 'B'), cons('A', 'B')))

assertEqual(eq('A', ['A', 'B']),
            undefined)
assertEqual(eq(['A', 'B'], ['A', 'B']),
            undefined)
