[Discuss] The RexSimplify about "a <> 1 and a = 2"

[xiong duan]

Hi followers.
    When I learned how to simplify the Rexnode in Calcite. I meet a problem
and need some help.
For example:
When we simplify  "a <> 1 or a = 1 [a is nullable]", (the result is
different according to how to treat the UNKNOW value) :

checkSimplify3_(        or(ne(vInt(0), literal(1)),        eq(vInt(0),
literal(1))),        "OR(IS NOT NULL(?0.int0), null)",        "IS NOT
NULL(?0.int0)",        "true");

But when I try to simplify "a<>1 and a = 2 [a is nullable]":

    checkSimplify3_(
            and(ne(vInt(0), literal(1)),
                    eq(vInt(0), literal(2))),
            "=(?0.int0, 2)",
            "=(?0.int0, 2)",
            "=(?0.int0, 2)");

And I think this result should be:
 "a<>1 and a = 2 [a is nullable]":

UNKNOW AS TRUE: a IS NULL or a = 2
UNKNOW AS FALSE: a is NOT NULL and a =2
UNKNOW AS UNKNOW: CASE(IS NULL(a), null, a = 2)

So What did I misunderstand? It is a bug or intentional? Any feedback would
be appreciated.