theorem :: FINSEQ_1:98

for x1, x2, y1, y2 being object holds
( not {[x1,y1],[x2,y2]} is FinSequence or ( x1 = 1 & x2 = 1 & y1 = y2 ) or ( x1 = 1 & x2 = 2 ) or ( x1 = 2 & x2 = 1 ) )