Code to prove correctness of the leftpad program

• Naturals (for measuring the length of lists)

  • Addition
  • Subtraction

• Booleans (for equality- two terms of the same type are either equal or not)

  • Logical AND

• Equality typeclass (our leftpad will be polymorphic so the generic parameter must be an instance of the equality typeclass to be comparable)

• List (duh)

  • isPrefixOf
  • isSuffixOf
  • length
  • repeat
  • toString