shrink/fusion: don't count 'unzip' as using an array
comment wibbles
pretty: better handling of tuples
zips and unzips up to 9-tuples
fusion/aletD: always fuse unzips

More generally, consider the bound term when deciding whether to eliminate the let binding. At the moment this is just a special case checking for 'unzip' structures.
fix complexity of aletD

make sure to only call 'embedAcc' once on each of the bound/body expressions
export 'subTop' from substitution