``` error when applying the rule removal technique on rules: a(b(a(b(a(x))))) -> b(x) relative rules: x ->= a(a(b(b(x)))) to remove the rules a(b(a(b(a(x))))) -> b(x) x -> a(a(b(b(x)))) ``` the rule x ->= ... cannot be removed, and it does not have to https://github.com/TermCOMP/starexec-master/issues/76