x = 


x = nil


x = 
x.length  


if x == 
  puts 
else
  puts 
end
y = 'bc'
if x < y
  puts 
end


xx = x.dup
x == xx       
x.equal?(xx)  


if x.empty?
  puts 
end


p x << 


p xx = x[0..-2]
x[1,2] = 
p x


p y = .tr(, )


a = 
b = 
c = 
p d = a + b + c