Incredibilmente questo comando è nella versione light e non nella full:
consente di fare linee in coppia per i muri, con estremità e intersezioni, al volo: DLINE (double lines).
Mi vergogno di ammettere che non conscevo questo comando, forse perché normalmente lavoro con la versione full. Conoscevo la versione complessa MLINE che a mio avviso funziona piuttosto male (se non altro perché è rimasta a tempi anteriori al stb).Questa semplicemente consente di disegnare una serie di coppie di linee o archi paralleli (muri!) direttamente senza dover fare offset o quant'altro, con intersezioni e opzioni di chiusura dell'estremità, ma con entità semplici (linee ed archi).

Ci sono incappato per caso digitando male un comando alla tastiera sulla versione light di un collega.
Mi sembra incredibile che non sia disponibile nella versione full, ma ecco il relativo autolisp: double lines, per fortuna, altrimenti l'intero reparto di ingegneri software della nota casa andrebbe licenziato in blocco.

Ordunque: digitato il comando, fate attenzione alle opzioni, a cominciare dalla Width/larghezza che volete mantenere tra la coppia di segmenti, poi dovrete decidere l'allineamento con cui disegnare la doppia riga: se quellea di sinistra, destra, l'asse tra le due, o un offset (Dragline). Potrete decidere come terminare: con una lineetta che le unisca o lasciarle aperte. Potete cambiare l'amppiezza durante il tracciamento, e anche inserire archi.
E ora provate a farne un'altra e terminarla su un lato della prima: tadaa! trim automatico all'intersezione (solo per intersezioni a T, non a X, mi dispiace…) Comunque meglio che passare ore a trimmare i disegni.

Mi dispiace constatare che una volta usato l'arco il trim automatico smette di funzionare, e bisogna riavviare il cad, ma credo che disegnare archi capiti di rado.

Non so se le due versioni siano identiche (light e lisp - lo spero) ma incollo nel seguito le istruzioni scritte in testa all'autolisp:

DESCRIPTION
;;;     
;;;     This is a general purpose "double-line/arc" generator.  It performs 
;;;     automatic corner intersection cleanups, as well as a number of other 
;;;     features described below.
;;;  
;;;     The user is prompted for a series of endpoints.  As they are picked 
;;;     "DLINE"  segments are drawn on the current layer.  Options are 
;;;     available for changing the Width of the DLINE, specifying whether
;;;     or not to Snap to existing lines or arcs, whether or not to 
;;;     Break the lines or arcs when snapping to them, and which of the 
;;;     following to do:  
;;;     
;;;     Set the global variable dl:ecp to the values listed below:
;;;  
;;;     Value  Meaning
;;;     ---------------------------
;;;       0    No end caps
;;;       1    Start end cap only
;;;       2    Ending end cap only
;;;       3    Both end caps
;;;       4    Auto ON -- Cap any end not on a line or arc.
;;;       
;;;     The user may choose to back up as far as the beginning of the command 
;;;     by typing "U" or "Undo", both of which operate as AutoCAD's "UNDO 1" 
;;;     does.
;;;     
;;;     Curved DLINE's are drawn using the AutoCAD ARC command and follow as 
;;;     closely as possible its command structure for the various options.
;;;  
;;;----------------------------------------------------------------------------
;;;   OPERATION
;;;
;;;     The routine is executed, after loading, by typing either DL or DLINE
;;;     at which time you are presented with the opening line and menu of
;;;     choices:
;;;     
;;;       Dline, Version 1.11, (c) 1990-1992 by Autodesk, Inc.  
;;;       Break/Caps/Dragline/Offset/Snap/Undo/Width/<start point>: 
;;;     
;;;     Typing Break allows you to set breaking of lines and arcs found at
;;;     the start and end points of any segment either ON or OFF.
;;;     
;;;       Break Dline's at start and end points?  OFF/<ON>:
;;;     
;;;     Typing Caps allows you to specify how the DLINE will be finished 
;;;     off when exiting the routine, per the values listed above.
;;;     
;;;       Draw which endcaps?  Both/End/None/Start/<Auto>:
;;;       
;;;     The default of Auto caps an end only if you did not snap to an arc
;;;     or line.
;;;     
;;;     Typing Dragline allows you to set the location of the dragline
;;;     relative to the centerline of the two arcs or lines to any value
;;;     between - 1/2 of "tracewid" and + 1/2 of "tracewid".  (There is a
;;;     local variable you may set if you want to experiment with offsets
;;;     outside this range;  the results may not be correct, your choice.
;;;     See the function (dl_sao) for more information.)
;;;     
;;;       Set dragline position to Left/Center/Right/<Offset from center = 0.0>:
;;;     
;;;     Enter any real number or one of the keywords.  The value in the angle
;;;     brackets is the default value and changes as you change the dragline
;;;     position.
;;;     
;;;     Offset allows the first point you enter to be offset from a known
;;;     point.
;;;     
;;;       Offset from:  (enter a point)
;;;       Offset toward:    (enter a point)
;;;       Enter the offset distance:   (enter a distance or real number)
;;;  
;;;     Snap allows you to set the snapping size and turn snapping ON or OFF.
;;;     
;;;       Set snap size or snap On/Off.  Size/OFF/<ON>:
;;;       New snap size (1 - 10):
;;;     
;;;     The upper limit may be reset by changing the value of MAXSNP to a 
;;;     value other than 10.  Higher values may be necessary for ADI display
;;;     drivers, but generally, you should keep this value somewhere in the 
;;;     middle of the allowed range for snapping to work most effectively 
;;;     in an uncluttered drawing, and toward the lower end for a more 
;;;     cluttered drawing.  You may also use object snap to improve your 
;;;     aim.
;;;     
;;;     This feature allows you to very quickly "snap" to another line or arc, 
;;;     breaking it at the juncture and performing all of the intersection 
;;;     cleanups at one time without having to be precisely on the line, i.e., 
;;;     you can be visually one the line and it will work, or you can use 
;;;     object snap to be more precise.
;;;     
;;;     Undo backs you up one segment in the chain of segments you are drawing,
;;;     stopping when there are no more segments to be undone.  All of the 
;;;     necessary points are saved in lists so that the DLINE will close, cap,
;;;     and continue correctly after any number of undo's.
;;;     
;;;     Width prompts you for a new width.
;;;     
;;;       New DLINE width <1.0000>:
;;;       
;;;     You may enter a new width and continue the DLINE in the same direction
;;;     you were drawing before;  if you do this, connecting lines from the
;;;     endpoints of the previous segment are drawn to the start points of 
;;;     the new segment.
;;;     
;;;     If you press RETURN after closing a DLINE or before creating any
;;;     DLINE's, you will see this message:
;;;     
;;;       No continuation point -- please pick a point.  
;;;       Break/Caps/Dragline/Offset/Snap/Undo/Width/<start point>:  
;;;     
;;;     After you pick the first point, you will see this set of options:
;;;     
;;;       Arc/Break/CAps/CLose/Dragline/Snap/Undo/Width/<next point>:
;;;       
;;;     Picking more points will draw straight DLINE segments until either 
;;;     RETURN is pressed or the CLose option is chosen.
;;;     
;;;     CLose will close the lines if you have drawn at least two segments.
;;;     
;;;     Selecting Arc presents you with another set of choices:
;;;     
;;;       Break/CAps/CEnter/CLose/Dragline/Endpoint/Line/Snap/Undo/Width/<second point>:
;;;     
;;;     All of the options here are the same as they are for drawing straight
;;;     DLINE's except CEnter, Endpoint, and Line.
;;;     
;;;     The default option, CEnter, and Endpoint are modeled after the ARC
;;;     command in AutoCAD and exactly mimic its operation including all of
;;;     the subprompts.  Refer to the AutoCAD reference manual for exact usage.
;;;     
;;;     The Line option returns you to drawing straight DLINE segments.
;;;     
;;;     Snapping to existing LINE's an ARC's accomplishes all of the trimming 
;;;     and extending of lines and arcs necessary, including cases where arcs 
;;;     and lines do not intersect.  In these cases a line is drawn from either;
;;;     a point on the arc at the perpendicular point from the center of the 
;;;     arc to the line, to the line, or along the line from the centers of the
;;;     two arcs that do not intersect at the points where this line crosses
;;;     the two arcs.  In this way, we ensure that all DLINE's can be closed
;;;     visually.
;;;     
;;;     Breaking will not work unless Snapping is turned on.