Maxima: suppress `linenum` in both input and output prompt -

the maxima documentation reads:

maxima automatically constructs label each computed expression concatenating outchar , linenum.

http://maxima.sourceforge.net/docs/manual/maxima_4.html#outchar

it describes how customize inchar , outchar, there line number included. know useful referencing expressions later, when putting post on e.g. stackoverflow, line numbers aren't important, want omit them.

(also, purely cosmetic, makes inputs misalign little.)

instead of this:

(%i9) 1 + 1; (%o9)                                  2 (%i10) 2 + 2; (%o10)                                 4 

i want this:

(%i) 1 + 1; (%o)                                   2 (%i) 2 + 2; (%o)                                   4 

how can customize maxima prompt suppress line number?