gistfile1.txt

[2] (pry) main: 0> def multiply(x, y)
[2] (pry) main: 0*   2 * x * y
[2] (pry) main: 0* end  
=> nil
[3] (pry) main: 0> alias old_multiply multipy
NameError: undefined method `multipy' for class `Object'
from (pry):5:in `<main>'

[4] (pry) main: 0> alias old_multiply multiply
=> nil
[5] (pry) main: 0> def multiply(x, y)
[5] (pry) main: 0*   puts "wrapping old multiply"
[5] (pry) main: 0*   old_multiply(x, y)
[5] (pry) main: 0* end  
=> nil
[6] (pry) main: 0> multiply(2, 3)
wrapping old multiply
=> 12