You can put the red and blue disks on themselves

>INVENTORY
You are carrying:
  A blue disk
  A red disk

>PUT RED DISK ON RED DISK
Nothing happens.

>PUT BLUE DISK ON BLUE DISK
Nothing happens.

>INVENTORY
You are empty handed.

The problem is that DISC-FCN will move PRSO into PRSI without checking that they are the same.

There is a check for that in V-PUT (It will print "You can you do that?"), but that's not called here.

the-infocom-files / starcross

You can put the red and blue disks on themselves #47