Help:=proc(): print(`MergeLists(L1,L2),MergeSort(L)`):end:

#MergeLists(L1,L2): merges two increasing lists
MergeLists:=proc(L1,L2) :

if L1=[] then
 RETURN(L2):
elif L2=[] then
 RETURN(L1):
fi:

if L1[1]<=L2[1] then
 RETURN([L1[1],op(MergeLists([op(2..nops(L1),L1)],L2))]):

else
 RETURN([L2[1],op(MergeLists([op(2..nops(L2),L2)],L1))]):
fi:
end:

#MergeSort(L): Merge Sort
MergeSort:=proc(L)
local L1,L2:
if L=[] or nops(L)=1 then
 RETURN(L):
fi:

L1:=[op(1..trunc(nops(L)/2),L)]:
L2:=[op(trunc(nops(L)/2)+1..nops(L),L)]:

L1:=MergeSort(L1):
L2:=MergeSort(L2):

MergeLists(L1,L2):
end: