Hans Milton, thank you for your example, it works.
Eric Rimbey, I use Mathematica 9. Concerning you opinion on default values, I have to think it over.
An example:
In[1]:= f[a_ : 50, b_ : 60, OptionsPattern[{c -> 70}]] := {a, b, OptionValue[c]} In[2]:= f[10, 20] Out[2]= {10, 20, 70} In[3]:= f[10] Out[3]= {10, 60, 70} In[4]:= f[] Out[4]= {50, 60, 70} In[5]:= f[10, 20, c -> 3] Out[5]= {10, 20, 3}
