Here is a term in the lambda calculus: λy.y. Input a term that is alpha-equivalent to this term, and that uses no bound variables that are bound in this term:

• Use single lowercase letters, such as f, g, x, y, z, for variables.
• For applications, write terms next to each other; so for example x y is x applied to y.
• For abstractions, you can use \ as your lambda, so for example \x.x is the function that returns its input unmodified. Or, if you prefer, you can click this button to copy a lambda to your clipboard, and then write λx.x instead. Binchicken doesn't care whether you use \ or λ; it's your call!
• Finally, if you run into bugs or difficulties, please let me know! Screenshots are very much appreciated.