ReplaceRepeated (//.)¶ Repeatedly applies transformation rules until no more changes occur. $ wo 'f[f[f[2]]] //. f[x_] -> x' 2 $ wo 'f[f[f[f[2]]]] //. f[2] -> 2' 2 $ wo 'f[f[f[2]]] //. f[x_] -> x + 1' 5