Maude example showing overlapping subsorts

t.maude

fmod T is
    var XX : X .
    var YY : Y .
    var TT : Thing .

    sort Thing .
    op a : -> Thing [ctor] .
    op b : -> Thing [ctor] .
    op _|_ : Thing Thing -> Thing [ctor] .

    sort X .
    subsort X < Thing .
    mb a | TT : X .

    sort Y .
    subsort Y < Thing .
    mb TT | a : Y .
endfm

match [5] XX <=? a | a . *** expected: a solution. actual: no solution.  BAD
match [5] XX <=? a | b . *** expected: a solution. actual: a solution.   OK
match [5] XX <=? b | a . *** expected: no solution. actual: no solution. OK
match [5] XX <=? b | b . *** expected: no solution. actual: no solution. OK

match [5] YY <=? a | a . *** expected: a solution. actual: a solution.   OK
match [5] YY <=? a | b . *** expected: no solution. actual: no solution. OK
match [5] YY <=? b | a . *** expected: a solution. actual: a solution.   OK
match [5] YY <=? b | b . *** expected: no solution. actual: no solution. OK