Thankyou - I have later found them in the Manual, but even then, nothing seemed to work. I tried it both before selecting the tool, and with a tool (a Circle, and Simple Extrude) selected.
So, having just read the above, I tried again, the computer having been turned off in the meantime. Same thing: no access to the IB, but obviously I've no way of determining what the fault is, nor locate and correct it. I have examined the various Set-up menus carefully and they contain nothing to help here.
I don't know if it's related, but recently there were some peculiar network problems with access to TC or its Forum, apparently in a server belonging to Cloudflare (whoever they are) in London. Also, this Forum forgot my password for me and I've just had to set a new one.