Finding all increasing subsequences in Ruby

all_increasing_subsequences.rb

class Array
  def powersets
    inject([[]]){ |ps, el| ps + ps.map{ |e| e + [el] } }
  end

  def increasing?
    each_with_index do |el, i|
      break if i == size - 1
      return false unless el < self[i + 1]
    end
    true
  end
  
  def all_increasing_subsequences
    powersets[1..-1].select(&:increasing?).sort_by(&:length)
  end

  def sequences
    (0...size).flat_map { |i| (i...size).map { |j| self[i..j] } }
  end

  def sole?
    size == 1
  end

  def monotonic?
    each_with_index do |el, i|
      break if i == size - 1
      return false unless el == self[i + 1] - 1
    end
    true
  end

  def monotonic_increasing_sequences
    sequences.reject(&:sole?).select(&:monotonic?).sort_by(&:size).uniq.reverse!
  end
end