theorem Th66: :: FINSEQ_1:66

for x1, x2, x3, x4 being set
for p being FinSequence st p = ((<*x1*> ^ <*x2*>) ^ <*x3*>) ^ <*x4*> holds
( len p = 4 & p . 1 = x1 & p . 2 = x2 & p . 3 = x3 & p . 4 = x4 )