The command you want requires the GAP package HAPprime,
no longer being developed: its repository at GitHub is archived,
and some of the code has been migrated to HAP.

That said, you can still install it by downloading the package's
compressed tarball and unpacking it in your `~/.gap/pkg/`

folder
(after creating it if necessary).

To do that on CoCalc, open a CoCalc terminal and run
the following commands (skip the initial `$`

on each line
which represents the prompt):

```
$ GAP_PKG='~/.gap/pkg'
$ mkdir -p $GAP_PKG
$ cd $GAP_PKG
$ URL=https://files.gap-system.org/gap48/tar.gz/packages
$ TGZ=happrime-0.6.tar.gz
$ wget $URL/$TGZ
$ tar xf $TGZ
```

Then you can use the desired GAP command, either directly in GAP
or in Sage (via `gap`

or, better, `libgap`

) after loading the package
HAPprime.

In Sage:

```
sage: libgap.LoadPackage("happrime")
#I HAP warning: Set BROWSER_PATH manually if needed.
true
sage: G = libgap.SmallGroup(64, 134)
sage: R = libgap.ResolutionPrimePowerGroupRadical(G, 10)
sage: R
Resolution of length 10 in characteristic 2 for <pc group of size 64 with 6 generators> .
No contracting homotopy available.
A partial contracting homotopy is available.
```

What about

`G.ResolutionPrimePowerGroupRadical(10)`

?Apparently, this is not in GAP but in HAP ?

@FrédéricC It gives me the same error. And yes, as far as I understand this function comes from HAP but I don't really grasp what that means. I've tried to add the line gap.LoadPackage("hap") but it yields a similar "hap must have a value" error.

And in fact, not in HAP (that sage has) but in HAPprime (that sage does not have)