[m-users.] mmc --debug and mdb usage problems

[Razetime]

All the programs I have tried to compile are from here:
https://github.com/razetime/aoc/tree/main/16
Using the guide:
https://mercurylang.org/information/doc-release/mercury_user_guide/Quick-overview.html#Quick-overview
My installation was from the debian package repository, given here:
http://dl.mercurylang.org/deb/. My OS is Ubuntu 20.02 (fossa)
I would like to know if I am doing any steps wrong, or my install is
not correct.

I have tried to compile and build a program with imported module,
which gives the following error:
$ mmc --debug --make a07
mercury_compile: error: the Mercury standard library cannot be found in grade
  `asm_fast.gc.debug'.

mmc --debug a01 runs quietly with no output, and mdb ./a01 after that
just runs the program as is with no debugger controls appearing.