Warning: CHC: Empty array "pop" happens here.
Counterexample:
arr = []
a = 0x0
x = 0
success = true

Transaction trace:
test.constructor()
State: arr = []
test.f(0x0, 1)
    a.call{value: x}("") -- untrusted external call
  --> input.sol:13:3:
   |
13 | 		arr.pop();
   | 		^^^^^^^^^
