CROSSOVER:
*
*******
* *** *
y*******x // cover with 8 dominoes
*****
X*Y
X/Y both protrude implies x/y both protrude:
A
BBBACCC
* DAE *
FFFDGEHHH
*DGE*
*G*
X protrudes implies x protrudes:
*
ABBBCCC
A DDD *
*AEEEFGGG
HHHF*
**F
Neither protrudes implies neither protrudes:
*
AAABBBC
* DDD C
*EEEFFFC* // unsymmetrical tiling!
GGG**
HHH