$! the measure of the divergent is not sufficient
D x y
C x (y a)

$! the measure of the divergent is badly not sufficient
D x y
C x (a. y (a b))

$! algorithm diverges
D x y x
C x x x
C y y y a

$! algorithm diverges reaching the previous configuration!
D x y
C x x
C y y a

$! stepping on useless arg
D x y
C x x
C y a b