These
efficient and flexible blocks can
be constructed by cycling a sequence
such as
x-xx---x or x---x-xx, to ensure that any interval or pair appears at least once.
The columns
and rows can then be rearranged to
get alternate, equivalent versions.
The smaller blocks with 7 to 12 selections
contain duplicate pairs.
TimeBlock13
has no duplicate pairs, but still
guarantees 1 or 2 lines of 3 if 5
correct.
And finally, for the record, but no symmetry between rows and columns, MindSpaceBlock16 covers 16 matches in 20 columns to guarantee any pair appears once at least!
