added add_local/add_global; index props (for add_local only); added could_unify;
added add_local/add_global;
index props (for add_local only);
added could_unify;

MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle,MerelyAPseudonym/isabelle