make cpair_less, cpair_defined_iff into iff rules; add lemma csplit1
make cpair_less, cpair_defined_iff into iff rules; add lemma csplit1

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