Mitchell-style forcing, with small working parts and collections of\n models as side conditions, and gap-one simplified morasses

We give a modification of Mitchell's technique for adding objects of size\n$\\omega_2$ with conditions with finite working parts in which the collections\nof models used as side conditions are very highly structured, arguably making\nthem more wieldy. We use one such forcing (essentially a `pure side conditions'\nforcing) to answer affirmatively the question, asked independently by Shelah\nand Velleman in the late 1980s, as to whether a $(\\kappa^+,1)$-simplified\nmorass can be added by a forcing with working parts of size $<\\kappa$.\n