Program Display;

USES
    crt;

VAR
   N3,N2,N1,N0:Boolean;

BEGIN
   clrscr;

     FOR N3:= False TO True DO
         FOR N2:= False TO True DO
             FOR N1:= False TO True DO
                 FOR N0:= False TO True DO
   BEGIN

     Write('--');

     IF N1 THEN
        IF N0 THEN
           IF (N3 or N2) THEN Write(' a ') ELSE Write('   ')
        ELSE
            Write(' a ')
     ELSE
        IF N0 THEN
           Write(' a ')
        ELSE
            IF (N3 or N2) THEN Write(' a ') ELSE Write ('   ');


     IF (N1 or not(N2)) THEN Write(' b ') ELSE Write('   ');


     IF N1 THEN
        IF N0 THEN
           Write(' c ')
        ELSE
            Write(' c ')
     ELSE
        IF N0 THEN
           IF (N2 or N3) THEN Write(' c ') ELSE Write('   ')
        ELSE
            Write(' c ');


     IF N1 THEN
        IF N0 THEN
           IF (N2 or N3) THEN Write(' d ') ELSE Write('   ')
        ELSE
            IF not(N2 or N3) THEN Write(' d ') ELSE Write('   ')
     ELSE
        IF N0 THEN
           IF not(N3) THEN Write(' d ') ELSE Write('   ')
        ELSE
            IF (N2 or N3) THEN Write(' d ') ELSE Write('   ');


     IF N1 THEN
        IF N0 THEN
           IF (N2 or N3) THEN Write(' e ') ELSE Write('   ')
        ELSE
            Write('   ')
     ELSE
        IF N0 THEN
           Write(' e ')
        ELSE
            Write('   ');


     IF N1 THEN
        IF N0 THEN
           Write(' f ')
        ELSE
            Write('   ')
     ELSE
        IF N0 THEN
           IF (N2 or N3) THEN Write(' f ') ELSE Write('   ')
        ELSE
            IF (N2 or N3) THEN Write(' f ') ELSE Write('   ');


     IF N1 THEN
        IF N0 THEN
           Write(' g ')
        ELSE
            IF not(N2 or N3) THEN Write(' g ') ELSE Write('   ')
     ELSE
        IF N0 THEN
           Write(' g ')
        ELSE
            IF (N2 or N3) THEN Write(' g ') ELSE Write('   ');


     WriteLn;

   END
END.

    Source: geocities.com/v.iniestra/apuntes/dis_log

               ( geocities.com/v.iniestra/apuntes)                   ( geocities.com/v.iniestra)