The code below, found at 
http://github.com/eregon/RPCFN4/blob/master/solutions/benoit_daloze.rb (with 
the last two lines added for testing it) produced the error:
Polynomials.rb:15:in `each_with_index': no block given (LocalJumpError)
The erronious line is flagged with #=================
Debugging indicates that @ceof is an Array.
What's up?

# Benoit Daloze
# Ruby Programming Challenge For Newbies #4
# pretty-print polynomials
#
# My solution use Enumerable#inject to build the String,
# with every "monomial" splitted in 3 parts : sign, coefficient and variable
class Polynomial
  def initialize(coef)
    raise ArgumentError, "Need at least 2 coefficients" if coef.size < 2
    @coef = coef
  end

  def to_s
    return '0' if @coef.all? { |c| c == 0 }
    @coef.each_with_index.inject("") { |s, (coef, i)|   # 
<===================================
      pow = @coef.length-1-i
      if coef == 0
 s
      else
 s +
 (coef > 0 ? '+' : '-') + # sign
 (coef.abs == 1 && pow != 0 ? '' : coef.abs.to_s) + # coef
 (pow < 2 ? 'x'*pow : "x^#{pow}") # var
      end
    }.sub(/^\+/, "")
  end
end

 p = Polynomial.new( [1, 2] )
 puts p



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