class MoreMath::ContinuedFraction

method) the +x+ will be the second argument of the block.
argument to the block. If a_n is dependent on an +x+ value (see the call
block has to return the value for a_n when +n+ is passed as the first
has to respond to an integer index n >= 0 and return the value a_n. The
This method either takes a block or an argument +arg+. The argument +arg+

def for_a(arg = nil, &block)
  if arg and !block
    @a = arg
  elsif block and !arg
    @a = block
  else
    raise ArgumentError, "exactly one argument or one block required"
  end
  self
end