This page contains a gallery of symmetric forms of different kinds that you
can make of bridged Tetrominoes. The number of solutions for each form is large
but not unreachable to calculate with a powerful computer.

The tile set of the 22 bridged Tretominoes harbours an inner symmetry aspect.
The tiles can be arranged in a pairwise relationship, if you exchange diagonal
and horizontal connections in the construction. The naming of the tiles reflect
this relationship. The next picture shows this with a tile style where is becomes
very appearent.

The tile pair E1-E2 shows a very subtle irregularity. The tile E2 is open at
one side and therefore not symmetric where the tile E1 is fully symmetric. If
we would choose the open form for E1, the number of solutions increases by a
factor of four.

Square Ring with 29,785,696 * 8 solutions
found with1,884,934,044,496 recursion cycles

Square with Window ?? * 8 solutions

Swiss Cheese ?? * 8 solutions

?? * 8 solutions

?? * 8 solutions

?? * 8 solutions

?? * 8 solutions

?? * 8 solutions

?? * 8 solutions

?? * 4 solutions

This form is based on the fact, that every number divisible by four is difference
of two square numbers. In this case it's 4 * 22 = 88 = 13^{2} - 9^{2}.