Memorable tricks

If this occurs to you, don't spend hours like me hacking /etc/ssh/sshd_config but check "All users" in System preferences > Sharing. Moreover, to apply the changes you must restart the server and you can do so quickly also in Sharing by checking out and in "Remote login". Indeed the behaviour is kind of buggy because you are still prompted for password and there is nothing to see in ssh -v. 

The problem Sharing files from Mac to Mac (both on Mac OS X El Capitan) on the same local network, I cannot see a target user's Library (as opposed to his other directories).  The solution For the target user,  ~/Library is accessible, with the same permissions as other directories, but appears greyed out . Let the target user do:  in Finder, View > Show View Options, check Show Library Folder. Remark No problem with nfs server on target Mac. Reference Mac OS X file sharing

Start form fresh kernel: In[21]:= Quit[] This is an indefinite Sum (see the documentation of Sum): In[1]:= Sum[x[i],i] Out[1]= Underscript[\[Sum], i]x[i] In[2]:= Sum[Indexed[x,i],i] Out[2]= Underscript[\[Sum], i]Subscript[x, i] This evaluates wrongly: In[3]:= Sum[_,i] Out[3]= i _ and seems to break Sum: In[4]:= Sum[y[i],i] Out[4]= i _ In[5]:= Sum[Indexed[y,i],i] Out[5]= i _ although all the sums that were previously evaluated are still correct: In[6]:= Sum[x[i],i] Out[6]= Underscript[\[Sum], i]x[i] In[7]:= Sum[Indexed[x,i],i] Out[7]= Underscript[\[Sum], i]Subscript[x, i] Conclusions : - Sum is broken by Sum[_,i], - the kernel has some cache. Indeed there is a cache and it can be cleared In[8]:= ClearSystemCache[] but this has no effect on Sum: In[11]:= Sum[x[i],i] Out[11]= Underscript[\[Sum], i]x[i] In[12]:= Sum[y[i],i] Out[12]= i _

No search in the Option inspector. No spell-checking. No Autocompletion. No Function template. No Documentation. No Edit > Redo. No Cell > NotebookHistory. No File > Print. No possibility of saving as demonstration. Save as HTML does not work.

After some googling about cell numbering, I ended up being able to number inline formula, text, output, but not input cells. Of course, there is already the In[_] numbering or the possibility of numbering the corresponding output cell (if it exists), so that input cell numbering may not be necessary after all. However, when input is reevaluated, the In[_] numbering changes and the output cell numbering is lost so input cell numbering is really important. According to CounterTutorial.nb by P. J. Hinton, 1998: A CounterBox[ ] can appear only in a TextData[ ] expression of a cell, so that means you can use them only [in] cell styles associated with headings and body text.  They cannot be used in the contents of typeset math cells. Therefore, input cell numbering may not be so easy.  However: You can inspect the low level trickery that is used by opening up the notebook's style sheet and unformatting the prototype cell for NumberedEquation.  I won't go into too mu...