def double(n):
    return 2*n
    
def pluralize(st):
    return st+'s'

#def mapDouble(nums):
#  return map(double, nums)

def mapPluralize(strings):
  return map(pluralize, strings)

def myMap(f, elts):
    result = []
    for e in elts:
        result.append(f(e))
    return result

def square(n):
    return n*n

def mapSquare(nums):
    return map(square, nums)

def upper(st):
    return st.upper()

def mapUpper(strings):
    return map(upper, strings)
    
def mapDouble(nums):
    # Locally define the double function within mapDouble. 
    # This may only be used inside mapDouble and not outside
    def double(n):
      return 2*n
    return map(double,nums)

def mapScale(factor,nums):
  # Can't define this outside of mapScale, because
  # it needs to refer to parameter named "factor"
  def scale(n):
    return factor*n
  return map(scale, nums)

def mapPrefixes(string):
  # Can't define this outside of mapPrefixes, because
  # it needs to refer to parameter named "string"
  def prefix(i):
    return string[:i+1]
  return map(prefix, range(len(string)))

def mapPreConcat(pre, strings):
    def concat(i):
        return pre+strings[i]
    return map(concat, range(len(strings)))