a$ = ">Rosetta_Example_1
THERECANBENOSPACE
>Rosetta_Example_2
THERECANBESEVERAL
LINESBUTTHEYALLMUST
BECONCATENATED"

i = 1
while i <= len(a$)
  if mid$(a$,i,17) = ">Rosetta_Example_" then
    print
    print mid$(a$,i,18);": ";
    i = i + 17
   else
    if asc(mid$(a$,i,1)) > 20 then print mid$(a$,i,1);
  end if
  i = i + 1
wend