Implement a Python function called Euler that takes as input a list of pairs representing an undirected graph and returns a list presenting a sequence of edges constituting and Euler path if there is one. If no such path exits, return the empty list. the input needs to be as shown below.

Theres other answers out there but they have been copy pasted. the inputs do not work in any of them so please do not just paste those same ones as the input must be the same provided below. Thank you so much!

input: Euler[ [1,2], [1,3], [3,4], [4,5] ]