21.4. A bubble-sort algorithm is defined in the following manner:

procedure bubblesort;

var i, t, integer;

begin repeat until ta[1]

t:a[1];

for j: 2 to n do if a[j-1]  a[j] then begin t:a[j-1];

a[j-1]:a[j];

a[j]:t;

end endrep end Partition the design into subfunctions, and define a set of conditions that would enable you to prove that this algorithm is correct.