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 strongly closed criterion
not linear
result: MAYBE
time: 0 msec.