Martin Gardner published the tetrads found by Scott Kim in Scientific American 4 / 1977.
In 1977 Scott Kim was a student at Stanford University.
According to the 'Journal of Recreational Mathematics 10, no. 4, 1977/1978' [3] many readers found simply connected Tetrads.
Tetrads made by Frank Rubin (Tetrad D, I), Karl Scherer (I) and Scott Kim (J) are shown in JRM.
(Ortwin Schenker sent me a copy of the articles in 2024, thank you.)
A polyomino tetrad with one hole and 5 tetrads with no holes were presented in Gardner's article.
The following 6 tetrads with congruent regions were drawn without colors and without grid in the article.
A
B
C
D
E
F
Scott Kim made an excellent job. Therefore Martin Gardner had very few questions left for the readers.
His questions (in all cases tetrads with no hole are meant):
(a) Is there a tetrad with convex outside border?
(b) Is there a tetrad made of polyiamonds of order less than 10?
(c) Is there a tetrad made of polyominoes of order less than 12?
(d) Is there a tetrad which is bilateral symmetric and made of bilaterally symmetric polygons with less than 22 sides?
Question (a) could not be answered until today.
The answer on question (b) is no. Exhaustive computer searches by George Sicherman [7] and others proved that 10 is the smallest order.
According to Martin Gardner, Walter Trump (the author of this website) was the only reader who could answer question (c) and found a tetrad made of polyominoes of order 11 before 1980. (Tetrad G) Robert Ammann, Greg Frederickson and Jean L. Loyer independently answered question (d) and found an 18-sided polygonal tetrad with bilateral symmetry. (Tetrad H)
G
H
The following tetrads were printed in JRM [3] in the shown way.
Tetrad I was independently found by Frank Rubin and Karl Scherer, tetrad J was found by Scott Kim.
I
J
B 
D 
F 
H 
J