theorem Th20: :: GFACIRC1:20

for x, y, z being set
for s being State of (GFA0CarryCirc (x,y,z))
for a1, a2, a3 being Element of BOOLEAN st a1 = s . x & a2 = s . y & a3 = s . z holds
( (Following s) . [<*x,y*>,and2] = a1 '&' a2 & (Following s) . [<*y,z*>,and2] = a2 '&' a3 & (Following s) . [<*z,x*>,and2] = a3 '&' a1 )