Triangular Progressions etc. have recently appeared in Word Ways 2009088, 2009167 and 1009285. In addition to words which form UPRIGHT triangles, other words form INVERTED triangles and, within each of these two forms, there are 3 categories.
Word Ways: Vol. 42
, Article 7.
Available at: https://digitalcommons.butler.edu/wordways/vol42/iss4/7