"a" -> "b"-
~"a" -> "b"+
"present.j" -> "present.k"-
~"present.j" -> "present.k"+
"present.k" -> "present.l"-
~"present.k" -> "present.l"+
@ "b" iscomb
@ "c" iscomb
@ "present.l" iscomb
connect "a" "present.P.a"
connect "b" "present.P.b"
connect "present.j" "present.Q.a"
connect "present.k" "present.Q.b"
connect "present.k" "present.R.a"
connect "present.l" "present.R.b"
connect "a" "present.w"
connect "b" "present.x"
connect "c" "present.y"
connect "d" "present.z"
