Added functions mk_cntxt_splitthm and inst_split which instantiate the split-rule before it is applied. Inserted some comments.
Added functions mk_cntxt_splitthm and inst_split which instantiate
the split-rule before it is applied.
Inserted some comments.

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