MAYBE
ignored inputs:
(COMMENT an explicit substitution calculus for lambda terms )
(COMMENT Example 43 of [ FG07 , doi:10.1016/j.ic.2006.12.002 ] )

NRS:
   [ (0):  |- (sub <[a](app <[]X,[]Y>),[]Z>) -> (app <(sub <[a][]X,[]Z>),(sub <[a][]Y,[]Z>)>),
     (1):  |- (sub <[a]a,[]X>) -> []X,
     (2): a#X |- (sub <[a][]X,[]Y>) -> []X,
     (3): b#Y |- (sub <[a](lam [b][]X),[]Y>) -> (lam [b](sub <[a][]X,[]Y>)) ]
Check confluence by orthogonality
abstract skeleton preserving
left-linear
check proper overlapping
a proper overlap exists
0-2
a#X,a#Y |- < (app <(sub <[a][]X,[]Y_1>),(sub <[a][]Y,[]Y_1>)>) <= (sub <[a](app <[]X,[]Y>),[]Y_1>) => (app <[]X,[]Y>) >
found proper overlaps
result: MAYBE
time: 2 msec.