A tetrad is a plane figure made of four congruent shapes,
joined so that each shares a boundary with each.
Here I show various minimal tetrads for polyiamonds.
The smallest polyiamond tetrads use 10-iamonds.
According to Karl Scherer, Frank Rubin may have found the first solution.
The purple solutions were found by
The smallest tetrad made from a polyiamond with mirror symmetry
The smallest tetrad made from a polyiamond with birotary symmetry
The smallest tetrads made from polyiamonds with horizontal mirror symmetry
The smallest tetrad made from a polyiamond with ternary symmetry
The smallest tetrads made from polyiamonds with ternary symmetry
about a vertex use 27-iamonds:
The smallest polyiamonds that form tetrads without being reflected
are these 10-iamonds:
They are also the smallest polyiamonds that form tetrads without
being rotated 60° or 180°.
The smallest holeless tetrad made from a polyiamond
with mirror symmetry uses 22-iamonds.
It was found independently by Robert Ammann, Greg Frederickson, and
Jean L. Loyer.
The smallest tetrads with a single one-cell hole
are formed by this 16-iamond:
The smallest tetrad with a single two-cell hole
is formed by this 17-iamond:
Last revised 2021-02-04.
Back to Polyform Tetrads
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Col. George Sicherman