theorem Th5: :: QUATERNI:12

for x1, x2, x3, x4, y1, y2, y3, y4 being Real st [*x1,x2,x3,x4*] = [*y1,y2,y3,y4*] holds
( x1 = y1 & x2 = y2 & x3 = y3 & x4 = y4 )