Ruby lambda Puzzle (question part)

In Ruby 1.9.1,

Question 1

irb(main):001:0> lambda_a = lambda do |x|
irb(main):002:1*   lambda do |y|
irb(main):003:2*     puts "Hello #{x} #{y}"
irb(main):004:2>   end
irb(main):005:1>   lambda do |z|
irb(main):006:2*     puts "Goodbye #{x} #{z}"
irb(main):007:2>   end
irb(main):008:1> end
=> #<Proc:0x223d780@(irb):1 (lambda)>
irb(main):009:0> lambda_a.(1).(2)
？？？

Question 2

irb(main):010:0> lambda_b = lambda do |x|
irb(main):011:1*   lambda do |y|
irb(main):012:2*     puts "Hello #{x} #{y}"
irb(main):013:2>   end
irb(main):014:1>   lambda do |z, zz|
irb(main):015:2*     puts "Goodbye #{x} #{z} #{zz}"
irb(main):016:2>   end
irb(main):017:1> end
=> #<Proc:0x1dfd680@(irb):10 (lambda)>
irb(main):018:0> lambda_b.(1).(2)
？？？