MAYBE
(ignored inputs)COMMENT submitted by: Hans Zantema
Rewrite Rules:
   [ a(b(a(?x))) -> b(a(b(?x))),
     b(a(b(?x))) -> a(b(a(?x))),
     a(c(a(?x))) -> c(a(c(?x))),
     c(a(c(?x))) -> a(c(a(?x))),
     a(d(a(?x))) -> d(a(d(?x))),
     d(a(d(?x))) -> a(d(a(?x))),
     b(c(?x)) -> c(b(?x)),
     c(b(?x)) -> b(c(?x)),
     b(d(?x)) -> d(b(?x)),
     d(b(?x)) -> b(d(?x)),
     d(c(?x)) -> c(d(?x)),
     c(d(?x)) -> d(c(?x)),
     p -> a(p),
     p -> b(p),
     p -> c(p),
     p -> d(p) ]
Apply Direct Methods...
Inner CPs:
   [ a(a(b(a(?x_1)))) = b(a(b(b(?x_1)))),
     a(b(c(a(c(?x_2))))) = b(a(b(c(a(?x_2))))),
     a(b(d(a(d(?x_4))))) = b(a(b(d(a(?x_4))))),
     b(b(a(b(?x)))) = a(b(a(a(?x)))),
     b(a(c(b(?x_6)))) = a(b(a(c(?x_6)))),
     b(a(d(b(?x_8)))) = a(b(a(d(?x_8)))),
     a(c(b(a(b(?x))))) = c(a(c(b(a(?x))))),
     a(a(c(a(?x_3)))) = c(a(c(c(?x_3)))),
     a(c(d(a(d(?x_4))))) = c(a(c(d(a(?x_4))))),
     c(c(a(c(?x_2)))) = a(c(a(a(?x_2)))),
     c(a(b(c(?x_7)))) = a(c(a(b(?x_7)))),
     c(a(d(c(?x_11)))) = a(c(a(d(?x_11)))),
     a(d(b(a(b(?x))))) = d(a(d(b(a(?x))))),
     a(d(c(a(c(?x_2))))) = d(a(d(c(a(?x_2))))),
     a(a(d(a(?x_5)))) = d(a(d(d(?x_5)))),
     d(d(a(d(?x_4)))) = a(d(a(a(?x_4)))),
     d(a(b(d(?x_9)))) = a(d(a(b(?x_9)))),
     d(a(c(d(?x_10)))) = a(d(a(c(?x_10)))),
     b(a(c(a(?x_3)))) = c(b(a(c(?x_3)))),
     b(b(c(?x_7))) = c(b(b(?x_7))),
     b(d(c(?x_11))) = c(b(d(?x_11))),
     c(a(b(a(?x_1)))) = b(c(a(b(?x_1)))),
     c(c(b(?x_6))) = b(c(c(?x_6))),
     c(d(b(?x_8))) = b(c(d(?x_8))),
     b(a(d(a(?x_5)))) = d(b(a(d(?x_5)))),
     b(b(d(?x_9))) = d(b(b(?x_9))),
     b(c(d(?x_10))) = d(b(c(?x_10))),
     d(a(b(a(?x_1)))) = b(d(a(b(?x_1)))),
     d(c(b(?x_6))) = b(d(c(?x_6))),
     d(d(b(?x_8))) = b(d(d(?x_8))),
     d(a(c(a(?x_3)))) = c(d(a(c(?x_3)))),
     d(b(c(?x_7))) = c(d(b(?x_7))),
     d(d(c(?x_11))) = c(d(d(?x_11))),
     c(a(d(a(?x_5)))) = d(c(a(d(?x_5)))),
     c(b(d(?x_9))) = d(c(b(?x_9))),
     c(c(d(?x_10))) = d(c(c(?x_10))),
     a(b(b(a(b(?x))))) = b(a(b(b(a(?x))))),
     b(a(a(b(a(?x))))) = a(b(a(a(b(?x))))),
     a(c(c(a(c(?x))))) = c(a(c(c(a(?x))))),
     c(a(a(c(a(?x))))) = a(c(a(a(c(?x))))),
     a(d(d(a(d(?x))))) = d(a(d(d(a(?x))))),
     d(a(a(d(a(?x))))) = a(d(a(a(d(?x))))) ]
Outer CPs:
   [ a(p) = b(p),
     a(p) = c(p),
     a(p) = d(p),
     b(p) = c(p),
     b(p) = d(p),
     c(p) = d(p) ]
Linear
(inner) Parallel CPs: (not computed)
unknown Toyama (Parallel CPs)
Direct Methods: Can't judge

Combined result: Can't judge
1283.trs: Failure(unknown CR)
(1 msec.)