theorem Th4: for x,y being FinSequence st x is U-valued & y is U-valued
holds (U-concatenation).(x,y)=x^y
proof
let x,y be FinSequence; set f=U-concatenation; assume x is U-valued &
y is U-valued; then reconsider xx=x, yy=y as FinSequence of U by Lm1;
f.(xx,yy)=xx^yy by Lm10; hence thesis;
end;
