I pushed on with the install, which is still not successful. Here are some more things that came up.
1. Installation refused to proceed without encrypted swap. Since this is for a laptop and I wanted suspend to disk I didn't want it encrypted. (On review, it looks as if I could encrypt as long as I don't choose random keys.) Refusing to proceed seems a bit draconian. Also, I am assuming that swap as a logical volume in an LVM volume group will work with the suspend feature. I'm not sure if that assumption is correct. 2. I walked most of the way through the encryption process with one logical volume, and then got the error "This build of -di does not include one or more programs that are required for partman_crypto to function correctly." Earlier in the installation process it asks what optional modules to load; I had picked dm-crypto but not some of the other ones (for the install attempt reported in my earlier message I selected mroe of these modules). I do not know if the error reflects a missing program in the installer, my failure to load the correct module, the fact that encrypting logical volumes doesn't work, or something else. 3. The significance of the optional modules was not entirely clear to me. My guess is they are not optional if you want to use certain features. Since the installation manual made no mention of this for encryption, for example, I wasn't sure. This may only be an issue in expert mode. 4. The installation manual says "First you will be given the opportunity to automatically partition either an entire drive, or available free space on a drive. This is also called “guided” partitioning. If you do not want to autopartition, choose Manual from the menu." It appears the only guided partitioning options available are for the whole disk. This was one reason I selected guided partitioning in my first attempt; the manual made me think it could handle just the free space. 5. If encrypting LVM logical volumes is supported, the installer menu item to encrypt a "physical volume" is inaccurate or at least incomplete. 6. Although I deselected the dekstop task, with only laptop and standard tasks selected, some X11 packages got downloaded. I'm not sure if that is by design. Ross