theorem Th47: :: MATRIX_0:47

for x1, x2, y1, y2 being object holds
( len ((x1,x2) ][ (y1,y2)) = 2 & width ((x1,x2) ][ (y1,y2)) = 2 & Indices ((x1,x2) ][ (y1,y2)) = [:(Seg 2),(Seg 2):] )