Okay, if it's as simple as just wanting to avoid inadvertantly overwriting function defintions, I suggest that you Protect your functions after you define them.

Why would someone want that? Because if you have a larger mathematica file and you inadvertently define the same function somehow below the first function, then the first function is overwritten by the second function, that is if you do not initialize the first function again (pressing enter+shift again on the first function) past calculations/plots will be based now on the new function defined after the old function. I see that the option is to have different names for the functions, such as: f1[x], f2[x], etc, so that you don't have to worry about writing Clear[f] and then initializing from the previous new function. It would have been good if the first function with the same name was not overwritten by the 2nd function with the same name, and the effect of the 2nd function starting from the definition of the 2nd function down and having no effect on what is defined above.

I see that it works also with Clear[f] You can look at the sequence number that I followed for In[1], In[2], etc - this was the running sequence.

So, the user must be careful to delete the definition of the new function and then to initialize the old function to be able to use the old function. And if he wants to use the new function again, he has to initialize the new function again... I thought there was a setting that would automatically take this into account.