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 Merge(A,p,q,r)
           n1=q-p+1;
           n2=r-q;
           for i<-1 to n1
               L[i]<-A[p+i-1]
           for j<-1 to n2
                R[j]<-A[q+j]
           L[n1+1]<-oo  ,   R[n2+1]<-oo   
               
           
           i<-1, j<-1
           for k<-p to r
              if L[i]<=R[j] then
                  A[k]<-L[i]
                  i<-i+1
              else
                  A[k]<-R[j]
                  j<-j+1
             
      
        MERGESORT(A,p,r)
           if p<r then
              q<-floor((p+r)/2)
              MERGESORT(A,p,q)
              MERGESORT(A,q+1,r)
              Merge(A,p,q,r)