first_minor

# File lib/matrix.rb, line 659
  def first_minor(row, column)
    raise RuntimeError, "first_minor of empty matrix is not defined" if empty?

    unless 0 <= row && row < row_count
      raise ArgumentError, "invalid row (#{row.inspect} for 0..#{row_count - 1})"
    end

    unless 0 <= column && column < column_count
      raise ArgumentError, "invalid column (#{column.inspect} for 0..#{column_count - 1})"
    end

    arrays = to_a
    arrays.delete_at(row)
    arrays.each do |array|
      array.delete_at(column)
    end

    new_matrix arrays, column_count - 1
  end