01 typedef int (*ptr)(); // pointer to int function
02 int H(ptr x, ptr y) // uses x86 emulator to simulate its input
03
04 int D(ptr x)
05 {
06 int Halt_Status = H(x, x);
07 if (Halt_Status)
08 HERE: goto HERE;
09 return Halt_Status;
10 }
11
12 void main()
13 {
14 H(D,D);
15 }

When H is a simulating termination analyzer based on an x86 emulator
within the x86utm operating system this is the execution trace of the
above code:

Line 14: main() calls H(D,D) that simulates D(D)

keeps repeating:
Line 06: simulated D(D) calls simulated H(D,D) that simulates D(D) ...

Simulation invariant:
D correctly simulated by H never reaches its own Line 09.

This enables H to abort its simulation of D and correctly report that
(its input) D correctly simulated by H never halts. The above is fully
operational code within the x86utm operating system.
https://github.com/plolcott/x86utm

*Broadening the Practical Scope of Software Termination Analysis*
https://www.researchgate.net/publication/369971402_Broadening_the_Practical_Scope_of_Software_Termination_Analysis

--
Copyright 2023 Olcott "Talent hits a target no one else can hit; Genius
hits a target no one else can see." Arthur Schopenhauer