(VAR X Y Z X1 X2 X3) (RULES active(and(true,X)) -> mark(X) active(and(false,Y)) -> mark(false) active(if(true,X,Y)) -> mark(X) active(if(false,X,Y)) -> mark(Y) active(add(0,X)) -> mark(X) active(add(s(X),Y)) -> mark(s(add(X,Y))) active(first(0,X)) -> mark(nil) active(first(s(X),cons(Y,Z))) -> mark(cons(Y,first(X,Z))) active(from(X)) -> mark(cons(X,from(s(X)))) mark(and(X1,X2)) -> active(and(mark(X1),X2)) mark(true) -> active(true) mark(false) -> active(false) mark(if(X1,X2,X3)) -> active(if(mark(X1),X2,X3)) mark(add(X1,X2)) -> active(add(mark(X1),X2)) mark(0) -> active(0) mark(s(X)) -> active(s(X)) mark(first(X1,X2)) -> active(first(mark(X1),mark(X2))) mark(nil) -> active(nil) mark(cons(X1,X2)) -> active(cons(X1,X2)) mark(from(X)) -> active(from(X)) and(mark(X1),X2) -> and(X1,X2) and(X1,mark(X2)) -> and(X1,X2) and(active(X1),X2) -> and(X1,X2) and(X1,active(X2)) -> and(X1,X2) if(mark(X1),X2,X3) -> if(X1,X2,X3) if(X1,mark(X2),X3) -> if(X1,X2,X3) if(X1,X2,mark(X3)) -> if(X1,X2,X3) if(active(X1),X2,X3) -> if(X1,X2,X3) if(X1,active(X2),X3) -> if(X1,X2,X3) if(X1,X2,active(X3)) -> if(X1,X2,X3) add(mark(X1),X2) -> add(X1,X2) add(X1,mark(X2)) -> add(X1,X2) add(active(X1),X2) -> add(X1,X2) add(X1,active(X2)) -> add(X1,X2) s(mark(X)) -> s(X) s(active(X)) -> s(X) first(mark(X1),X2) -> first(X1,X2) first(X1,mark(X2)) -> first(X1,X2) first(active(X1),X2) -> first(X1,X2) first(X1,active(X2)) -> first(X1,X2) cons(mark(X1),X2) -> cons(X1,X2) cons(X1,mark(X2)) -> cons(X1,X2) cons(active(X1),X2) -> cons(X1,X2) cons(X1,active(X2)) -> cons(X1,X2) from(mark(X)) -> from(X) from(active(X)) -> from(X) )