Argyle MOD 6

Author:   dominicbeesley
Category: Christmas Challenge
System:   BBC
Language: BASIC
Len source code: 53
Len exe file:    n/a
Len code only:   53
Instructions:
In B-em or BeebEm load the .ssd file (Disc->Load 0/2) and boot with 
shift-break (shift-F12) or type 
    CHAIN"PROGRAM"
at the BASIC > pompt 

Description:
    Draw a character at each position in the 19x19 grid
    at each character if (C+L) MOD 6 = 0 OR (C-L) MOD 6 = 0 then draw 
    a star. One term C+L draws a set of diagonal NW to SE lines the other
    NE to SW.
    The fact that logical TRUE in BBC BASIC is -1 is used to remove an IF

    VDU 32-10*(<logical>) will print a space if FALSE (0) or a * if TRUE -1

    The logic above is reduces by using a multiply in place of the OR and
    reducing the expression to get rid of a few characters 

Comments:
    An .ssd containing the program and a !BOOT file have been provided for
    convenience but have not been counted in the byte count.

    53 in decimal is 35 in hex - this seemed like a good place to stop
    optimising!