Code Verification with Dafny

Below we give, in Dafny syntax, an outline of the psp method with the accompanying specification.

You need to write Dafny code and any necessary annotations to implement psp and make sure that

Dafny verifies it

$.$

$$You must not add or change anything in the specification that is given to you.

You are not allowed to use loops for this problem.

method psp

$($

$$x : i n t

$,$

$$y : i n t

$)$

$$r e t u r n s

$($

$$x

$$

$$: i n t

$,$

$$y

$$

$$: i n t

$)$

e n s u r e s x

$$

$+$

$$y

$$

$=$

$=$

$$x

$+$

$$y && x

$$

$*$

$$y

$$

$<$

$0$

$\{$

$/$

$/$

$$Write a s u i t a b l e implemen t a ti on o f psp

$.$

$/$

$/$

$$You must not add o r change any thin g i n the s p e c i f i c a t i o n

$!$

$\}$

$$can you give me the dafny code for psp that should verify? you can comment out or include a main method to check.